…eadLoc

Ports the remaining TODO logic in the require-await rule from typescript-eslint:

- Report the function head range (modifiers through the opening `(` of params, or
  the `=>` token for arrow functions) instead of the whole function body
- Attach a `removeAsync` suggestion that:
  - removes the `async` keyword plus trailing whitespace while preserving
    trailing comments (mirrors `getTokenAfter(async, {includeComments: true})`)
  - unwraps `Promise<T>` to `T` in the return type annotation for non-generators
  - renames `AsyncGenerator` to `Generator` in the return type annotation for
    generators
  - inserts a leading `;` when removing `async` before `[` or `(` would change
    parsing due to ASI hazard (class computed methods, expression statements)
- Enable all previously commented-out `Suggestions` assertions in the test file
  and regenerate the snapshot

Extracts two reusable helpers to internal/utils/:

- `utils.GetFunctionHeadLoc` — port of typescript-eslint's getFunctionHeadLoc,
  placed next to the existing `GetForStatementHeadLoc`. Unblocks the
  `TODO(port): getFunctionHeadLoc` markers in promise_function_async and
  no_misused_promises.
- `utils.FindModifier` — returns the modifier node of a given kind, symmetric
  companion to `IncludesModifier`; the latter is now a thin wrapper over it.

Made-with: Cursor