Add Tokens newtype wrapper, TokenKind iterator (#11361)

## Summary

Alternative to #11237 

This PR adds a new `Tokens` struct which is a newtype wrapper around a
vector of lexer output. This allows us to add a `kinds` method which
returns an iterator over the corresponding `TokenKind`. This iterator is
implemented as a separate `TokenKindIter` struct to allow using the type
and provide additional methods like `peek` directly on the iterator.

This exposes the linter to access the stream of `TokenKind` instead of
`Tok`.

Edit: I've made the necessary downstream changes and plan to merge the
entire stack at once.

crates/ruff_python_parser/src/token.rs

@@ -228,6 +228,11 @@ pub enum Tok {
 }
 
 impl Tok {
+    #[inline]
+    pub fn kind(&self) -> TokenKind {
+        TokenKind::from_token(self)
+    }
+
     pub fn start_marker(mode: Mode) -> Self {
         match mode {
             Mode::Module | Mode::Ipython => Tok::StartModule,