[clang] [clang][Sema] Diagnose exceptions only in non-dependent context in discarded `try/catch/throw` blocks (PR #139859)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> So @Rajveer100 : I think I bottomed out with Aaron. I think the solution of 'create a function to diagnose these, but only if not in a dependent `DeclContext`', then call this both from where we do the current checking, plus during `TreeTransform` of these things is the 'right' way forward. So you're close!

Agreed, thank you for the discussion!

https://github.com/llvm/llvm-project/pull/139859