Allow extensions to fully control workspace symbol search (matching and highlights)

[sam-mccall]

For qualified workspace-symbols queries like llvm::Str, our language server returns results like {containerName: "llvm", name: "StringRef"}.

VSCode attempts to fuzzy-match the query (llvm::Str) against the name only (StringRef). Because this always fails, it doesn't display any results.

In #23509 it's suggested this is something extensions should deal with, but it's not clear what extensions can do. The provideWorkspaceSymbols extension point must return SymbolInformation which are then filtered by name. Adding the qualifier to name means it is displayed twice - once in name and once in containerName.

[bpasero]

I think this will be hard to get right because in your example there is :: used as separator and there is no way our fuzzy matcher would simply skip over this separator given it is very language specific.

I think the ideal solution is to let extensions not only return the matching symbols but also do the matching and return positions to highlight. We probably reached the end of what our generic solution can do.

[sam-mccall]

@bpasero Thanks! A couple of other options too:

• Splitting the query on the last run of punctuation would work well at least for the languages I'm familiar with: match the last segment against the name and previous text against containerName.
• code completion is analogous and allows for providing filterText specifically for the purposes of matching. (Though AIUI this complicates display)