feat(language-service): support multiple symbol definitions

[ayazhafiz]

In Angular, symbol can have multiple definitions (e.g. a two-way
binding). This commit adds support for for multiple definitions for a
queried location in a template.

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

[ayazhafiz]

Note that in some cases, there a symbol can have multiple of the same definition -- for example, in the attribute value of a two way binding. [(ngModel)]="prop" really expands to [ngModel]="prop" (ngModel)="prop=$event", so when the definition for prop is requested, it is twice-referencing the prop member of the template's component. I did not include pruning duplicate entries in this commit because the LSP engines I tested this on (Vim via CoC and VSCode) handled these cases gracefully, combining the two definitions, but we can add code to prune them if desired..

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}