[clang] [DebugInfo] Improve efficiency of CGDebugInfo by using PresumedLoc. (PR #164608)

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SergejSalnikov wrote:

No. Unfortunately I do not have any numbers. But doing multiple expansion calls for the same location seems inefficient.

The PR simply replaces `SourceLocation` with `PresumedLoc` so readability wise the code should be equivalent. But in fact we don't really need `SourceLocation` as we consume the data from `PresumedLoc` object. What is the point in storing SourceLocation then.

https://github.com/llvm/llvm-project/pull/164608