C++ 20 all the things (#39454)

Summary:
Pull Request resolved: facebook/react-native#39454

1. Build with C++ 20 everywhere.
2. Update folly in OSS build to avoid a warning, and let us opt out of heavy bits required for supporting coroutines (we are still more than a year behind).
3. Update the folly podspec for the new version of folly
4. Update the many, many, copy/pasted header search paths for folly dependencies to be able to resolve fmt, now exposed to folly headers
4. Replaces a deprecated atomic usage with equivalent.
5. Fixes a deprecated implicit capturing `this` by value in lambda (same behavior, added a TODO because it seems sus)

Changelog: [Internal]

Reviewed By: sammy-SC

Differential Revision: D49271685

fbshipit-source-id: 16610f7bcd1032d5796cc11f1cfa92a33d8c2593

Original-Commit: facebook/react-native@17154a6

template/template/ios/HelloWorld.xcodeproj/project.pbxproj

@@ -516,7 +516,7 @@
 			buildSettings = {
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_ANALYZER_LOCALIZABILITY_NONLOCALIZED = YES;
-				CLANG_CXX_LANGUAGE_STANDARD = "c++17";
+				CLANG_CXX_LANGUAGE_STANDARD = "c++20";
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
@@ -576,7 +576,7 @@
 					"$(OTHER_CFLAGS)",
 					"-DFOLLY_NO_CONFIG",
 					"-DFOLLY_MOBILE=1",
-					"-DFOLLY_USE_LIBCPP=1",
+					"-DFOLLY_USE_LIBCPP=1 -DFOLLY_CFG_NO_COROUTINES=1",
 				);
 				SDKROOT = iphoneos;
 			};
@@ -587,7 +587,7 @@
 			buildSettings = {
 				ALWAYS_SEARCH_USER_PATHS = NO;
 				CLANG_ANALYZER_LOCALIZABILITY_NONLOCALIZED = YES;
-				CLANG_CXX_LANGUAGE_STANDARD = "c++17";
+				CLANG_CXX_LANGUAGE_STANDARD = "c++20";
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
@@ -639,7 +639,7 @@
 					"$(OTHER_CFLAGS)",
 					"-DFOLLY_NO_CONFIG",
 					"-DFOLLY_MOBILE=1",
-					"-DFOLLY_USE_LIBCPP=1",
+					"-DFOLLY_USE_LIBCPP=1 -DFOLLY_CFG_NO_COROUTINES=1",
 				);
 				SDKROOT = iphoneos;
 				VALIDATE_PRODUCT = YES;