Currently when building an Angular project with `ngtsc`
and `flatModuleOutFile` enabled, the Ngtsc build will fail
if there are multiple source files as root file names.
Ngtsc and NGC currently determine the entry-point for multiple
root file names by looking for files ending with `/index.ts`.
This functionality is technically deprecated, but still supported
and currently breaks on Windows as the root file names are not
guaranteed to be normalized POSIX-like paths.
In order to make this logic more reliable in the future, this commit
also switches the shim generators and entry-point logic to the branded
path types. This ensures that we don't break this in the future.
PR Close#29453
1e5a818719