feat: add symbol code prefix in symbol picker

[dinhani]

Implements #5446.

Not sure if this is the best approach, but I like that it allows me to quickly filter symbols by typing things like func: or struc:.

It would also be possible to generate the type indicator according to the language_id, so for example we could have fn for Rust file, def for Ruby, fun for Kotlin and defaulting to something else when not covered.

[the-mikedavis]

Duplicate of #5943