refactor(completions): improve cursor position detection

[mhanberg]

[mhanberg]

way too slow

[mhanberg]

error raised in Sourceror.Range.get_end_pos_for_interpolation_segments

code located in my notes as it contains work code

[mhanberg]

Turns out most of the slowness comes from fetching the docs for every function and module.

Will omit those and fetch on the completionItem/resolve request