Add filters for the LSP symbol picker

[LeoniePhiline]

The symbol picker is largely useless to get an overview of symbols, e.g. methods in a class, as it is overflowing with small cruft (local variables).

I'd really like to see a symbol picker with a built-in symbol type filter.

[the-mikedavis]

Also see the discussion in #4687 which talks a little about the symbol picker