[clang] [Coverage][Expansion] handle nested macros in scratch space (PR #89869)

[Wentao Zhang via cfe-commits]

whentojump wrote:

Sorry for getting back this late.

I reverted the latest commit (using `SourceRange`) and addressed the earlier comment about updating region sloc only when they are changed.

And yes if you have better ideas about `getNonScratchExpansion` implementation you can please post a new PR.

https://github.com/llvm/llvm-project/pull/89869