[clang] [Sema] Fast-path simple plain auto deduction in DeduceAutoType (PR #188196)

[via cfe-commits]

heturing wrote:

> Did you run check-clang? I would expect there are lot of test failures regarding dependent contexts.
> 
> Also in case any AI agent is involved, please read the AI policy before we move forward. Thanks. https://llvm.org/docs/AIToolPolicy.html

I run check-clang, and all test passed. Running ninja check-all generates the same result.
I have read the AI policy and am aware of it.

https://github.com/llvm/llvm-project/pull/188196