[analysis_server] enhance generated code

[asashour]

As hinted in sdk/247557, formatting the generated files takes around 00:01:30.

There seems to be some areas of improvement:

• use a single function to write the union from all similar places
• the code of individual field inside canParse can also be unified

current

reporter.push('annotationId');
try {
  if (!obj.containsKey('annotationId')) {
    reporter.reportError('must not be undefined');
    return false;
  }
  final annotationId = obj['annotationId'];
  if (annotationId == null) {
    reporter.reportError('must not be null');
    return false;
  }
  if (annotationId is! String) {
    reporter.reportError('must be of type String');
    return false;
  }
} finally {
  reporter.pop();
}

to be

if (_validateString(obj, reporter, 'annotationId')) {
  return false;
}

• ? No need for the trailing commas in parameters
• No need for extra spaces which would be removed by the formatter
• No need to ''' for string literals

[asashour]

This CL changes the time to less than 2 seconds.

https://dart-review.googlesource.com/c/sdk/+/247966

[asashour]

This CL uses a single function per type for canParse. The generated code shrinks from 46K to 40K lines.

https://dart-review.googlesource.com/c/sdk/+/248009