[Diagnostics] Restore -Wdeprecated warning when user-declared copy assignment...

[Diagnostics] Restore -Wdeprecated warning when user-declared copy assignment operator is defined as deleted (PR45634)

Solves https://bugs.llvm.org/show_bug.cgi?id=45634
Be more agressive than GCC with -Wdeprecated-copy. Also provide -W(no-)deprecated-copy-user-provided-copy/dtor options to on/off this behaviour.

Reviewed By: Quuxplusone

Differential Revision: https://reviews.llvm.org/D79714