Implement proper diagnostic messages in SYCLPropagateAspectUsage pass

[AlexeySachkov]

This issue is to track a follow-up from #5348: currently proposed implementation emits diagnostics without source location, making them much less usable.

There is a way to propagate source location from clang FE down to a pass through srcloc metadata: D106030, D110364 and it should be adopted in our SYCL pass as well.

I'm submitting that as a separate issue to avoid overcomplicating an already huge review.

Related comments: first, second and the third

[AlexeySachkov]

Diagnostic messages from the pass were implemented in #6982