[clang][clang-scan-deps] Add support for extracting full module dependencies.

[clang][clang-scan-deps] Add support for extracting full module dependencies.

This adds experimental support for extracting a Clang module dependency graph
from a compilation database. The output format is experimental and will change.
It is currently a concatenation of JSON outputs for each compilation. Future
patches will change this to deduplicate modules between compilations.

Differential Revision: https://reviews.llvm.org/D69420