[clang] [Clang] Add thousands-separator to "cannot allocate array; evaluated array bound [...] exceeds the limit" diagnostic (PR #211785)

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Sirraide wrote:

> I don't think we should play whack-a-mole trying to find all the places we could potentially print a large integer value and update the diagnostic call sites. I think this is something the diagnostics engine should handle when deciding how to render an integer so that the behavior is consistent across diagnostics. Otherwise we'll have to do the same dance for `note_constexpr_new_too_large`, `err_attribute_size_too_large`, and so on.

Can we just enable that by default for all diagnostics? Or is there one where that’s obviously wrong for some reason?

https://github.com/llvm/llvm-project/pull/211785