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_whitespace/src/whitespace.rs

@@ -1,43 +0,0 @@
-/// Returns `true` for [whitespace](https://docs.python.org/3/reference/lexical_analysis.html#whitespace-between-tokens)
-/// characters.
-pub const fn is_python_whitespace(c: char) -> bool {
-    matches!(
-        c,
-        // Space, tab, or form-feed
-        ' ' | '\t' | '\x0C'
-    )
-}
-
-/// Extract the leading indentation from a line.
-pub fn leading_indentation(line: &str) -> &str {
-    line.find(|char: char| !is_python_whitespace(char))
-        .map_or(line, |index| &line[..index])
-}
-
-pub trait PythonWhitespace {
-    /// Like `str::trim()`, but only removes whitespace characters that Python considers
-    /// to be [whitespace](https://docs.python.org/3/reference/lexical_analysis.html#whitespace-between-tokens).
-    fn trim_whitespace(&self) -> &Self;
-
-    /// Like `str::trim_start()`, but only removes whitespace characters that Python considers
-    /// to be [whitespace](https://docs.python.org/3/reference/lexical_analysis.html#whitespace-between-tokens).
-    fn trim_whitespace_start(&self) -> &Self;
-
-    /// Like `str::trim_end()`, but only removes whitespace characters that Python considers
-    /// to be [whitespace](https://docs.python.org/3/reference/lexical_analysis.html#whitespace-between-tokens).
-    fn trim_whitespace_end(&self) -> &Self;
-}
-
-impl PythonWhitespace for str {
-    fn trim_whitespace(&self) -> &Self {
-        self.trim_matches(is_python_whitespace)
-    }
-
-    fn trim_whitespace_start(&self) -> &Self {
-        self.trim_start_matches(is_python_whitespace)
-    }
-
-    fn trim_whitespace_end(&self) -> &Self {
-        self.trim_end_matches(is_python_whitespace)
-    }
-}