[clang] [clang] Add tests for CWG issues about friend declaration matching (PR #106117)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

@cor3ntin Can you take another look? I added CWG1900 section to the PR description. Nothing has changes for other Core issues.

https://github.com/llvm/llvm-project/pull/106117