[clang][deps] Support object files

When a project uses PCH with explicit modules, the build will look like this:

1. scan PCH dependencies
2. explicitly build PCH
3. scan TU dependencies
4. explicitly build TU

Step 2 produces an object file for the PCH, which the dependency scanner needs to read in step 3. This patch adds support for this.

The `clang-scan-deps` invocation in the attached test would fail without this change.

Depends on D103516.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D103519