Adds a `typeArguments` method to the `Symbol` interface, cleaning up how
type parameters of a TypeScript type are currently found. This will be
necessary for providing completions for `$event` variables' properties
(#34570).
This commit also performs some fly-by cleanups seen while implementing
the `typeArguments` methods. There is more clean up to do in the
`typescript_symbols` file, but the scope of this commit didn't need to
get larger.
PR Close#34571
The following files are consumed only by the language service and do not
have to be in compiler-cli:
1. expression_diagnostics.ts
2. expression_type.ts
3. typescript_symbols.ts
4. symbols.ts
PR Close#33809
