Rename ruff_python_whitespace to ruff_python_trivia (#5886)

## Summary

This crate now contains utilities for dealing with trivia more broadly:
whitespace, newlines, "simple" trivia lexing, etc. So renaming it to
reflect its increased responsibilities.

To avoid conflicts, I've also renamed `Token` and `TokenKind` to
`SimpleToken` and `SimpleTokenKind`.

crates/ruff_python_formatter/src/comments/visitor.rs

@@ -13,7 +13,7 @@ use ruff_python_ast::source_code::{CommentRanges, Locator};
 // pre-order.
 #[allow(clippy::wildcard_imports)]
 use ruff_python_ast::visitor::preorder::*;
-use ruff_python_whitespace::is_python_whitespace;
+use ruff_python_trivia::is_python_whitespace;
 
 use crate::comments::node_key::NodeRefEqualityKey;
 use crate::comments::placement::place_comment;