Clangd update check chokes on Apple Clangd Versioning

Hi awesome clangd folks,

I was running a test, setting things up from scratch on a new mac with the "Check Updates" feature enabled, and clangd otherwise not installed except for the Apple one in `/usr/bin/clangd`

I noticed that running an update check then fails with the error, presumably because it's surprised to find the Apple version's different formatting.
```Failed to check for clangd update: Error: Couldn't parse clangd --version output: Apple clangd version 13.0.0 (clang-1300.0.27.3)```
My guess at the right behavior: Disregard the apple clangd because it seems to crash consistently and immediately when invoked by the plugin.

[Running "clangd: Download language server" from the command palate still works--and is probably the best workaround for getting things going from scratch.]

Not a problem for me personally, but I bet it'll trip up some macOS users getting started, so I thought I should give a heads up.

Thanks!
Chris

P.S. Tagging @sam-mccall for discussion since I think he wrote the original version in clangd/vscode-clangd#5. Sam, sorry to keep tagging you here, and hope that's okay. It's truly a super good feature!