[clang][modules][deps] Serialize inputs into PCMs using the "as requested" name

This patch changes the PCM serialization logic to refer to input files by their "requested" name. This fixes a bug where the dependency scanner reports the "final" file paths, which can result in failed explicit compiles due to the `module.modulemap` file not being surrounded by the expected framework directory structure.

Depends on D135634.

Reviewed By: benlangmuir, Bigcheese

Differential Revision: https://reviews.llvm.org/D135636