[clang] [clang-tools-extra] [lldb] [clang] implement CWG1980 and CWG2064: instantiation-dependency improvements (PR #190495)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Honestly, this is just too huge to review reasonably.  I'm not sure what we can do about this.  We need to figure out a way to split up the meaningful/useful changes from 'the rest' so that we can properly grok what is going on.

https://github.com/llvm/llvm-project/pull/190495