Default initialize properties in custom structs

Summary:
If a native module spec declares a custom type:

https://www.internalfb.com/code/fbsource/[f6aeb413dbc3]/xplat/js/RKJSModules/Libraries/hsr/tm/code/editable_object/NativeEditableObjectModule.js?lines=151-154

The codegen will generate a c++ struct for that type, like so:

```
template <typename P0, typename P1>
struct NativeEditableObjectModuleChangedProperty {
  P0 propertyPath;
  P1 value;

  bool operator==(const NativeEditableObjectModuleChangedProperty &other) const {
    return propertyPath == other.propertyPath && value == other.value;
  }
};
```

## Problem
People can sometimes forget to default initialize this struct:
- **Report:** [post](https://fb.workplace.com/groups/rn.support/permalink/28506993098922601/)
- **Diff facebook#1:** D74868762
- **Diff facebook#2:** D77182083


In this scenario, all the members contain garbage data.

## Changes
This diff ensures that all the members are always default initialized, like so:

```
template <typename P0, typename P1>
struct NativeEditableObjectModuleChangedProperty {
  P0 propertyPath{};
  P1 value{};

  bool operator==(const NativeEditableObjectModuleChangedProperty &other) const {
    return propertyPath == other.propertyPath && value == other.value;
  }
};
```

This way, even if you forget to default initailize the struct, the members will still be default initialized.

## Concerns/Risks
This could cause compilation issues in some of our existing native modules. (if one of the member types doesn't have a default constructor).

Code could start behaving differently, now that all the members are default initialized. (my hunch is that the risk from this causing a problem is low).

Changelog: [General][Changed] c++ tm codegen: Default initialize properties in custom structs

Reviewed By: christophpurrer

Differential Revision: D77315742

Author: RSNara

packages/react-native-codegen/e2e/deep_imports/__tests__/modules/__snapshots__/GenerateModuleH-test.js.snap

@@ -348,7 +348,8 @@ struct Bridging<NativeEnumTurboModuleStatusStrEnum> {
 
 template <typename P0>
 struct NativeEnumTurboModuleStateType {
-  P0 state;
+  P0 state{};
+
   bool operator==(const NativeEnumTurboModuleStateType &other) const {
     return state == other.state;
   }
@@ -389,11 +390,12 @@ struct NativeEnumTurboModuleStateTypeBridging {
 
 template <typename P0, typename P1, typename P2, typename P3, typename P4>
 struct NativeEnumTurboModuleStateTypeWithEnums {
-  P0 state;
-  P1 regular;
-  P2 str;
-  P3 num;
-  P4 lowerCase;
+  P0 state{};
+  P1 regular{};
+  P2 str{};
+  P3 num{};
+  P4 lowerCase{};
+
   bool operator==(const NativeEnumTurboModuleStateTypeWithEnums &other) const {
     return state == other.state && regular == other.regular && str == other.str && num == other.num && lowerCase == other.lowerCase;
   }
@@ -862,8 +864,9 @@ private:
 
 template <typename P0, typename P1>
 struct NativePartialAnnotationTurboModuleSomeObj {
-  P0 a;
-  P1 b;
+  P0 a{};
+  P1 b{};
+
   bool operator==(const NativePartialAnnotationTurboModuleSomeObj &other) const {
     return a == other.a && b == other.b;
   }
@@ -1055,7 +1058,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleAnimal &other) const {
     return name == other.name;
   }
@@ -1257,7 +1261,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleArraysAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleArraysAnimal &other) const {
     return name == other.name;
   }
@@ -1459,7 +1464,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleNullableAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleNullableAnimal &other) const {
     return name == other.name;
   }
@@ -1661,7 +1667,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleNullableAndOptionalAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleNullableAndOptionalAnimal &other) const {
     return name == other.name;
   }
@@ -1865,7 +1872,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleOptionalAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleOptionalAnimal &other) const {
     return name == other.name;
   }
@@ -2478,7 +2486,8 @@ struct Bridging<NativeEnumTurboModuleStatusStrEnum> {
 
 template <typename P0>
 struct NativeEnumTurboModuleStateType {
-  P0 state;
+  P0 state{};
+
   bool operator==(const NativeEnumTurboModuleStateType &other) const {
     return state == other.state;
   }
@@ -2519,11 +2528,12 @@ struct NativeEnumTurboModuleStateTypeBridging {
 
 template <typename P0, typename P1, typename P2, typename P3, typename P4>
 struct NativeEnumTurboModuleStateTypeWithEnums {
-  P0 state;
-  P1 regular;
-  P2 str;
-  P3 num;
-  P4 lowerCase;
+  P0 state{};
+  P1 regular{};
+  P2 str{};
+  P3 num{};
+  P4 lowerCase{};
+
   bool operator==(const NativeEnumTurboModuleStateTypeWithEnums &other) const {
     return state == other.state && regular == other.regular && str == other.str && num == other.num && lowerCase == other.lowerCase;
   }
@@ -2992,8 +3002,9 @@ private:
 
 template <typename P0, typename P1>
 struct NativePartialAnnotationTurboModuleSomeObj {
-  P0 a;
-  P1 b;
+  P0 a{};
+  P1 b{};
+
   bool operator==(const NativePartialAnnotationTurboModuleSomeObj &other) const {
     return a == other.a && b == other.b;
   }
@@ -3185,7 +3196,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleAnimal &other) const {
     return name == other.name;
   }
@@ -3387,7 +3399,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleArraysAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleArraysAnimal &other) const {
     return name == other.name;
   }
@@ -3589,7 +3602,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleNullableAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleNullableAnimal &other) const {
     return name == other.name;
   }
@@ -3791,7 +3805,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleNullableAndOptionalAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleNullableAndOptionalAnimal &other) const {
     return name == other.name;
   }
@@ -3995,7 +4010,8 @@ private:
 
 template <typename P0>
 struct NativeSampleTurboModuleOptionalAnimal {
-  P0 name;
+  P0 name{};
+
   bool operator==(const NativeSampleTurboModuleOptionalAnimal &other) const {
     return name == other.name;
   }

packages/react-native-codegen/src/generators/modules/GenerateModuleH.js

@@ -298,7 +298,7 @@ function createStructsString(
 
 template <${templateParameterWithTypename}>
 struct ${structName} {
-${templateMemberTypes.map(v => '  ' + v).join(';\n')};
+${templateMemberTypes.map(v => '  ' + v + '{};\n').join('')}
   bool operator==(const ${structName} &other) const {
     return ${value.properties
       .map(v => `${v.name} == other.${v.name}`)