[Clang] CWG 1394: Incomplete types as parameters of deleted functions

According to CWG 1394 and C++20 [dcl.fct.def.general]p2,
Clang should not diagnose incomplete types if function body is "= delete;".
For example:
```
struct Incomplete;
Incomplete f(Incomplete) = delete; // well-formed
```

Also close https://github.com/llvm/llvm-project/issues/52802

Differential Revision: https://reviews.llvm.org/D122981