[clangd][ObjC] Improve completions for protocols + category names
- Render protocols as interfaces to differentiate them from classes
since a protocol and class can have the same name. Take this one step
further though, and only recommend protocols in ObjC protocol completions.
- Properly call `includeSymbolFromIndex` even with a cached
speculative fuzzy find request
- Don't use the index to provide completions for category names,
symbols there don't make sense
Differential Revision: https://reviews.llvm.org/D132962