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/src/comments/shebang.rs

@@ -1,4 +1,4 @@
-use ruff_python_whitespace::{is_python_whitespace, Cursor};
+use ruff_python_trivia::{is_python_whitespace, Cursor};
 use ruff_text_size::{TextLen, TextSize};
 
 /// A shebang directive (e.g., `#!/usr/bin/env python3`).