[Clang] Static member initializers are not immediate escalating context. (#66021)

Per CWG2760, default members initializers should be consider part the
body of constructors, which mean they are evaluated in an immediate
escalating context.

However, this does not apply to static members.

This patch produces some extraneous diagnostics, unfortunately we do not
have a good way to report an error back to the initializer and this is a
pre existing issue

Fixes #65985
Fixes #66562