[cfe] Update CFE message to use 'null safety' instead of 'non-nullable'

Closes #42464

Change-Id: I2865cd4ff2fac3c40d5f8b8d26d6b958919682b8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/152481
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Jens Johansen <jensj@google.com>

Author: johnniwinther

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -7850,7 +7850,7 @@ const Code<Null> codeStrongModeNNBDButOptOut = messageStrongModeNNBDButOptOut;
 const MessageCode messageStrongModeNNBDButOptOut = const MessageCode(
     "StrongModeNNBDButOptOut",
     message:
-        r"""A library can't opt out of non-nullable by default, when in nnbd-strong mode.""");
+        r"""A library can't opt out of null safety by default, when using sound null safety.""");
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeSuperAsExpression = messageSuperAsExpression;

pkg/front_end/messages.yaml

@@ -1186,7 +1186,7 @@ Unspecified:
   template: "#string"
 
 StrongModeNNBDButOptOut:
-  template: "A library can't opt out of non-nullable by default, when in nnbd-strong mode."
+  template: "A library can't opt out of null safety by default, when using sound null safety."
 
 AbstractNotSync:
   template: "Abstract methods can't use 'async', 'async*', or 'sync*'."

pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart.outline.expect

@@ -1,7 +1,7 @@
 //
 // Problems in component:
 //
-// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart: Error: A library can't opt out of non-nullable by default, when in nnbd-strong mode.
+// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart: Error: A library can't opt out of null safety by default, when using sound null safety.
 //
 library /*isNonNullableByDefault*/;
 import self as self;

pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart.strong.expect

@@ -1,7 +1,7 @@
 //
 // Problems in component:
 //
-// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart: Error: A library can't opt out of non-nullable by default, when in nnbd-strong mode.
+// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart: Error: A library can't opt out of null safety by default, when using sound null safety.
 //
 library /*isNonNullableByDefault*/;
 import self as self;

pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart.strong.transformed.expect

@@ -1,7 +1,7 @@
 //
 // Problems in component:
 //
-// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart: Error: A library can't opt out of non-nullable by default, when in nnbd-strong mode.
+// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_dill/strong_lib.dart: Error: A library can't opt out of null safety by default, when using sound null safety.
 //
 library /*isNonNullableByDefault*/;
 import self as self;

pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong.dart.outline.expect

@@ -10,7 +10,7 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong_lib.dart:1:1: Error: A library can't opt out of non-nullable by default, when in nnbd-strong mode.
+// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong_lib.dart:1:1: Error: A library can't opt out of null safety by default, when using sound null safety.
 // // @dart = 2.7
 // ^^^^^^^^^^^^^^
 //

pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong.dart.strong.expect

@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong_lib.dart:1:1: Error: A library can't opt out of non-nullable by default, when in nnbd-strong mode.
+// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong_lib.dart:1:1: Error: A library can't opt out of null safety by default, when using sound null safety.
 // // @dart = 2.7
 // ^^^^^^^^^^^^^^
 //

pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong.dart.strong.transformed.expect

@@ -12,7 +12,7 @@ library /*isNonNullableByDefault*/;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong_lib.dart:1:1: Error: A library can't opt out of non-nullable by default, when in nnbd-strong mode.
+// pkg/front_end/testcases/nnbd/strong_lib_not_ok_from_source/strong_lib.dart:1:1: Error: A library can't opt out of null safety by default, when using sound null safety.
 // // @dart = 2.7
 // ^^^^^^^^^^^^^^
 //