This commit adds "find references" functionality to the Ivy integrated
language service. The basic approach is as follows:
1. Generate shims for all files to ensure we find references in shims
throughout the entire program
2. Determine if the position for the reference request is within a
template.
* Yes, it is in a template: Find which node in the template AST the
position refers to. Then find the position in the shim file for that
template node. Pass the shim file and position in the shim file along
to step 3.
* No, the request for references was made outside a template: Forward
the file and position to step 3.
3. (`getReferencesAtTypescriptPosition`): Call the native TypeScript LS
`getReferencesAtPosition`. For each reference that is in a shim file, map those
back to a template location, otherwise return it as-is.
PR Close#39768
Andrew Scott