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_ast/src/whitespace.rs

@@ -1,7 +1,7 @@
 use ruff_text_size::{TextRange, TextSize};
 use rustpython_parser::ast::Ranged;
 
-use ruff_python_whitespace::is_python_whitespace;
+use ruff_python_trivia::is_python_whitespace;
 
 use crate::source_code::Locator;