[clang] [clang] Fix CTAD not work for C++ explicit type conversion (functional annotation). (PR #75779)

[Haojian Wu via cfe-commits]

hokein wrote:

> Can you please update your summary to explain the problem and how the fix addresses the problem.
> 
> This is usually what goes into the git log and we want those to be as descriptive as possible but also it help code reviewers to understand what they are reviewing quicker.

Thanks, I have updated the description with more details. 

https://github.com/llvm/llvm-project/pull/75779