[clangd] Provide suggestions with invalid config keys

Update the config file warning when an unknown key is detected which is likely a typo by suggesting the likely key.
This won't suggest a key that has already been seen in the block.

Appends the fix to the diag, however right now there is no support for presenting that fix to the user.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D92990