[clang][deps] Support inferred modules

This patch adds support for inferred modules to the dependency scanner.

Effectively a cherry-pick of https://github.com/apple/llvm-project/pull/699 authored by @Bigcheese with libclang and other changes omitted.

Contains following changes:

1. [Clang][ScanDeps] Ignore __inferred_module.map dependency.
  * This shows up with inferred modules, but it doesn't exist on disk, so don't report it as a dependency.

2. [Clang][ScanDeps] Use the module map a module was inferred from for inferred modules.

Also includes a smoke test that uses clang-scan-deps output to perform an explicit build. There's no intention to duplicate whatever `test/Modules` contains, just to verify the produced command-line does "work" (with very loose definition of work).

Split from D100934.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D102495