[clang] [Clang][AST] fix crash in mangle lambda expression (PR #78896)

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cor3ntin wrote:

Thanks for this patch.
Can you add a release note?

Does this fix any of these issues ? (if so, can you add test for them?

#76481 
#70064
#63271 
#61939
#45441

https://github.com/llvm/llvm-project/pull/78896