feat(language-service): Add diagnostics to suggest turning on strictTemplates

[kyliau]

This PR creates a way for the language server to retrieve compiler options
diagnostics via languageService.getCompilerOptionsDiagnostics().

This will be used by the language server to show a prompt in the editor if
users don't have strictTemplates or fullTemplateTypeCheck turned on.

Ref angular/vscode-ng-language-service#1053

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?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.io application / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[josephperrott]

LGTM

[atscott]

reviewed-for: public-api

[AndrewKushnir]

Reviewed-for: public-api

[zarend]

👍

I did some bike-shedding on the exact copy of the diagnostic, but that's not a blocker for me :).

[kyliau]

presubmit: http://test/OCL:353126924:BASE:353126943:1611274712720:8d8cb1db

[petebacondarwin]

Reviewed-for: public-api

[jessicajaniuk]

@kyliau This PR has conflicts with the 11.1.x branch. it's been retargeted to minor and merged into master only. Could you create a patch-only version of this PR to get it into 11.1.x?

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