[clang] [clang] Fix assertion failures involving code completion with delayed default arguments and exception specifications (PR #203794)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

@Sirraide Curious do you have a good idea of how we can know when we need `ConsumeCodeCompletionTok` set to `true`? 

https://github.com/llvm/llvm-project/pull/203794