[clang-tools-extra] [clangd] Add tweak to add pure virtual overrides (PR #139348)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> LGTM if HighCommander4 is happy.

Apologies, folks, I'm backlogged on reviews and probably won't have time to look at this for a while. If you're looking for a clangd reviewer, perhaps one of our other clangd maintainers, @llvm-beanz or @kadircet, could help with this one. 

https://github.com/llvm/llvm-project/pull/139348