feat(completions): basic scoring algorithm for tables

[juleswritescode]

This PR tries to improve the existing pg_completions crate – autocompletions!

The goal was to autocomplete table names based on the input:

1. select * from us should put the users table before the emails table
2. select * from private.u should put the private.uncommon before the public.users table

And whoopdidoopdie, it works.

An overview of the changes:

• Separated the types into Builder & Context as well as CompletionItem + CompletionRelevance to rank them (stolen from rust-analyzer)
• Removed some unnecessary lifetimes
• The CompletionBuilder now returns the tower_lsp::CompletionItem data structure
• Added some integation tests
• Made sure all crates use the workspace's tower-lsp version
• Added a small README.md to the pg_completions crate
• Added a small script that prints the tree-sitter tree of an sql file

[psteinroe]

very nice! just one thing about the api boundary. thanks for doing this!!

[psteinroe]

Awesome, thanks for working on the feedback!