[analyzer] Make logic for interpreting messages.yaml file sharable with CFE.

Moves the following top level declarations, as well as other
declarations they depend on, from
`pkg/analyzer/tool/messages/error_code_info.dart` into
`package:analyzer_utilities`, so that they can be imported by the CFE's
diagnostic code generator:

- `frontEndMessages`
- `placeholderPattern`
- `FrontEndErrorCodeInfo`

There is no functional change.

In a follow-up CL, I will modify
`pkg/front_end/tool/generate_messages_lib.dart` to use these
declarations.

Change-Id: I6a6a69642230f0b943ccaf800c1f9e569c5b7579
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447982
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/analyzer/test/src/fasta/message_coverage_test.dart

@@ -7,11 +7,11 @@ import 'dart:io' as io;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer_testing/package_root.dart' as package_root;
+import 'package:analyzer_utilities/messages.dart';
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
-import '../../../tool/messages/error_code_info.dart';
 import '../../generated/parser_test_base.dart';
 
 main() {

pkg/analyzer/test/verify_diagnostics_test.dart

@@ -6,6 +6,7 @@ import 'package:analyzer/diagnostic/diagnostic.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/utilities/package_config_file_builder.dart';
 import 'package:analyzer_testing/utilities/utilities.dart';
+import 'package:analyzer_utilities/messages.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';