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/Cargo.toml

@@ -13,7 +13,7 @@ license = { workspace = true }
 [lib]
 
 [dependencies]
-ruff_python_whitespace = { path = "../ruff_python_whitespace" }
+ruff_python_trivia = { path = "../ruff_python_trivia" }
 ruff_text_size = { workspace = true }
 
 anyhow = { workspace = true }