[clang] [Clang] [Tests] Refactor most unit tests to use DRAV instead (PR #115132)

[via cfe-commits]

Sirraide wrote:

CI on Windows seems to be broken trying to check out the branch:
```console
> git fetch -v --prune -- origin 0dd745286a124f7142d827810be5185abdc196cf
POST git-upload-pack (112 bytes)
>From https://github.com/llvm/llvm-project
 * branch                      0dd745286a124f7142d827810be5185abdc196cf -> FETCH_HEAD
> git checkout -f 0dd745286a124f7142d827810be5185abdc196cf
error: unable to unlink old 'clang/lib/AST/Decl.cpp': Invalid argument
error: unable to unlink old 'clang/lib/Serialization/ASTReaderDecl.cpp': Invalid argument
HEAD is now at 0dd745286a12 [Tests] Refactor most tests to use the dynamic visitor
```

https://github.com/llvm/llvm-project/pull/115132