[messages] Create a utility to migrate to literate diagnostic reporting API.

Adds the file `use_literate_api_in_analyzer.dart`. This script reads
the analyzer source files and identifies any places where the old
diagnostic reporting API is being used, e.g.:

    _diagnosticReporter.atNode(
      node,
      diag.deprecatedExtend,
      arguments: [element.name!],
    );

And refactors the code to use the new "literate" diagnostic reporting
API, e.g.:

    _diagnosticReporter.report(
      diag.deprecatedExtend.withArguments(typeName: element.name!).at(node),
    );

The idea is to automate the majority of the migration from the old to
the new diagnostic reporting API by taking care of the most
straightforward cases. More complex cases are skipped; they will have
to be migrated manually. In particular, any call site that contains
one of the following things will be left alone:

- A diagnostic code that isn't a direct reference to a diagnostic code
  constant (e.g., in the above example, `diag.deprecatedExtend` is ok
  because it refers directly to the `deprecatedExtend` constant).

- An argument list that isn't a list literal, or is a list literal
  containing flow control or spreads (e.g., in the above example,
  `[element.name!]` is ok because it's a simple list literal with no
  flow control or spreads).

- A comment somewhere inside the invocation. These are left to human
  translation so that the meaning of the comment can be preserved.

The script also skips translation of any diagnostic codes that use the
placeholder parameter names `p0`, `p1`, `p2`, etc. The rationale is
that if we start using the placeholder names now, then in the future
when we want to assign more reasonable parameter names, refactoring
will be more difficult. In future CLs, I plan to give better names to
some of these placeholder parameters, and then re-run the script to
allow more migration to occur.

Change-Id: I6a6a696404b42ca67e5208cb4e80de17e485551c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/467385
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

https://dart.googlesource.com/sdk/+/eddba24b96bfe8dc08b4124529276706c1e82237