[clang] [Clang][Sema] Mark decomposition decl invalid for explicit array type (PR #210964)

[Shengxin Pei via cfe-commits]

TPPPP72 wrote:

It is quite strange that the existing diagnostic mechanism relies on the `valid` flag. To thoroughly resolve this issue, it is inevitable that we need to re-examine the entire diagnostic workflow and use a unified `setInvalid`, just as I mentioned earlier. It is foreseeable that the workload will likely be substantial and exceed the capabilities of new contributors.

https://github.com/llvm/llvm-project/pull/210964