feat(language-service): modularize error messages

[ayazhafiz]

This commit performs a modularization of the Language Service's existing
diagnostic messages. Such a modularization has two primary advantages:

• Centralization and decoupling of error messages from the code that
  generates them makes it easy to add/delete/edit diagnostic messages,
  and allows for independent iteration of diagnostic messages and
  diagnostic generation.
• Prepares for additional features like annotating the locations where a
  diagnostic is generated and enabling the configuration of which
  diagnostics should be reported by the language service.

Although it would be preferable to place the diagnostics registry in an
independent JSON file, for ease of typing diagnostic types as an enum
variant of 'ts.DiagnosticCategory', the registry is stored as an object.

Part of #32663.

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Feature
• Refactoring (no functional changes, no api changes)

Does this PR introduce a breaking change?

• Yes
• No

[ayazhafiz]

Going through this I realized that a lot of the diagnostic messages are not actually ever tested for their generation. I will add tests for all of them in a future commit.

[kyliau]

A few minor comments, otherwise LGTM.

[josephperrott]

LGTM

[atscott]

Hi @ayazhafiz, would you mind rebasing with master to resolve the merge conflict?

[atscott]

Hey @ayazhafiz, there's now a lint error for the commits. Can you take a look?

INVALID COMMIT MSG: fixup! test(language-service): differentiate feature and internal infra tests
=> ERROR: Unable to find match for fixup commit among prior commits:
feat(language-service): modularize error messages

[ayazhafiz]

Hey @ayazhafiz, there's now a lint error for the commits. Can you take a look?

Should be fixed :)

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