Closes
https://github.com/zed-industries/zed/pull/31229#issuecomment-2906946881

Follow
https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#diagnosticTag

> Clients are allowed to render diagnostics with this tag faded out
instead of having an error squiggle.

and do not underline any unnecessary diagnostic at all.

Release Notes:

- Fixed clangd's inactive regions diagnostics excessive highlights