Some declaration files may not be referenced from an entry-point's
main typings file, as it may declare types that are only used internally.
ngcc has logic to include declaration files based on all source files,
to ensure internal declaration files are available.
For packages following APF layout, however, this logic was insufficient.
Consider an entry-point with base path of `/esm2015/testing` and typings
residing in `/testing`, the file
`/esm2015/testing/src/nested/internal.js` has its typings file at
`/testing/src/nested/internal.d.ts`. Previously, the declaration was
assumed to be located at `/esm2015/testing/testing/internal.d.ts` (by
means of `/esm2015/testing/src/nested/../../testing/internal.d.ts`)
which is not where the declaration file can be found. This commit
resolves the issue by looking in the correct directory.
PR Close#33875
985cadb73d