[llvm] [clangd] Support square bracket escaping in Annotations (PR #69379)

[Sam McCall via llvm-commits]

sam-mccall wrote:

The usual workaround for this is to use the digraph `<:` in place of `[`. Does this work for your case?

I'd prefer not to add a second escaping mechanism if the existing one does work, maybe we should document it though.

https://github.com/llvm/llvm-project/pull/69379