[clang] [clang] Add tests for CWG1800-1804 (PR #77509)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

This PR also updates status for CWG437, which is a follow-up to #77372.
Nothing wrong with the tooling, just my mistake separating output of make_cxx_dr_status from changes I already had for complete-class context DRs.

https://github.com/llvm/llvm-project/pull/77509