[clang][deps] Generate '-fmodule-file=' only for direct dependencies

The `clang-scan-deps` tool currently generates `-fmodule-file=` command-line arguments for the whole transitive closure of modular dependencies. This is not necessary, we only need to provide the direct dependencies on the command line. Information about transitive dependencies is stored within the `.pcm` files of direct dependencies. This makes the command lines shorter, but should be a NFC otherwise (unless there are bugs in the loading mechanism for explicit modules).

Depends on D120465.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D118915