Adds support for `getDefinitionAt` when called on a templateUrl
property assignment.
The currrent architecture for getting definitions is designed to be
called on templates, so we have to introduce a new
`getTsDefinitionAndBoundSpan` method to get Angular-specific definitions
in TypeScript files and pass a `readTemplate` closure that will read the
contents of a template using `TypeScriptServiceHost#getTemplates`. We
can probably go in and make this nicer in a future PR, though I'm not
sure what the best architecture should be yet.
Part of angular/vscode-ng-language-service#111
PR Close#32238
ayazhafiz