[clang] [SourceManager] Expose max usage of source location space as a Statistic (PR #96292)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

> LGTM. Please wait a couple of days before landing to give a chance to other folks for reviewing.

What would be a rationale to hold it off? It's perfectly within the [policy](https://llvm.org/docs/CodeReview.html#must-code-be-reviewed-prior-to-being-committed) to submit patches like this without too many reviewers and instead resolve any questions post-commit.

I would be happy to revert or update if people raise questions, it just seems like too much wait time for a patch that does not change much.

https://github.com/llvm/llvm-project/pull/96292