[clang] [clang] Extract in-memory module cache writes from `ASTWriter` (PR #190062)

[NAKAMURA Takumi via cfe-commits]

chapuni wrote:

This triggers inconsistency in incremental builds.
Could you add a cleanup into `clang/test/Driver/modules-driver-dep-graph.cpp`?

```
// RUN: rm -rf %t
```

https://github.com/llvm/llvm-project/pull/190062