Show results for "Go to symbol in workspace" incrementally

[stefanhaller]

When having multiple language servers, it would be useful to show results for "Go to symbol in workspace" as soon as they are available instead of waiting for all language servers to be done providing theirs. This is similar to what was done for hover providers in #137714.

Why is this needed? I'm using both clangd and the python language server at the same time. When using "Go to symbol in workspace" to look up a C++ symbol, clangd provides results almost instantly. However, pylance takes forever to provide symbols (on the order of minutes, not seconds), which makes the feature basically unusable for looking up C++ symbols, unless I disable the python language server.

I do realize that this may have many of the same problems mentioned in the similar request for completion (see #107343 (comment)), so suggestions for other workarounds would be much appreciated.

[stefanhaller]

Related to #105870.