Switch starlark to tree-sitter-starlark?

[auscompgeek]

Back in #44 we added Starlark support, reusing tree-sitter-python since Starlark's grammar is a subset of Python 2's.

Since then, https://github.com/tree-sitter-grammars/tree-sitter-starlark was created. It might be a good idea to switch to using it instead?

[pokey]

Definitely, tho we may no longer get it for free, depending whether the parse tree differs significantly from tree-sitter-python