feat!: Set `composite` in `tsconfig-google.json`

Documentation: https://www.typescriptlang.org/tsconfig/#composite

- Fixes `rootDirectory`-related issues:
  - https://www.typescriptlang.org/tsconfig/#rootDir
  - https://github.com/google/gts/issues/573
- Sets `declaration: true`:
  - https://www.typescriptlang.org/tsconfig/#declaration
- Sets `incremental: true`:
  - https://www.typescriptlang.org/tsconfig/#incremental
