Allow bindings to be created and referenced within annotations (#7885)

## Summary

Given:

```python
baz: Annotated[
    str,
    [qux for qux in foo],
]
```

We treat `baz` as `BindingKind::Annotation`, to ensure that references
to `baz` are marked as unbound. However, we were _also_ treating `qux`
as `BindingKind::Annotation`, which meant that the load in the
comprehension _also_ errored.

Closes https://github.com/astral-sh/ruff/issues/7879.

crates/ruff_linter/resources/test/fixtures/pyflakes/F821_18.py

@@ -0,0 +1,19 @@
+"""Test bindings created within annotations."""
+
+from typing import Annotated
+
+foo = [1, 2, 3, 4, 5]
+
+
+class Bar:
+    # OK: Allow list comprehensions in annotations (i.e., treat `qux` as a valid
+    # load in the scope of the annotation).
+    baz: Annotated[
+        str,
+        [qux for qux in foo],
+    ]
+
+
+# OK: Allow named expressions in annotations.
+x: (y := 1)
+print(y)

crates/ruff_linter/resources/test/fixtures/pyflakes/F821_19.py

@@ -0,0 +1,21 @@
+"""Test bindings created within annotations under `__future__` annotations."""
+
+from __future__ import annotations
+
+from typing import Annotated
+
+foo = [1, 2, 3, 4, 5]
+
+
+class Bar:
+    # OK: Allow list comprehensions in annotations (i.e., treat `qux` as a valid
+    # load in the scope of the annotation).
+    baz: Annotated[
+        str,
+        [qux for qux in foo],
+    ]
+
+
+# Error: `y` is not defined.
+x: (y := 1)
+print(y)

crates/ruff_linter/src/checkers/ast/mod.rs

@@ -1168,13 +1168,14 @@ where
                                 range: _,
                             }) = slice.as_ref()
                             {
-                                if let Some(expr) = elts.first() {
+                                let mut iter = elts.iter();
+                                if let Some(expr) = iter.next() {
                                     self.visit_expr(expr);
-                                    for expr in elts.iter().skip(1) {
+                                }
+                                for expr in iter {
                                     self.visit_non_type_definition(expr);
                                 }
                                 self.visit_expr_context(ctx);
-                                }
                             } else {
                                 debug!("Found non-Expr::Tuple argument to PEP 593 Annotation.");
                             }
@@ -1618,10 +1619,12 @@ impl<'a> Checker<'a> {
     fn handle_node_store(&mut self, id: &'a str, expr: &Expr) {
         let parent = self.semantic.current_statement();
 
+        // Match the left-hand side of an annotated assignment, like `x` in `x: int`.
         if matches!(
             parent,
             Stmt::AnnAssign(ast::StmtAnnAssign { value: None, .. })
-        ) {
+        ) && !self.semantic.in_annotation()
+        {
             self.add_binding(
                 id,
                 expr.range(),

crates/ruff_linter/src/rules/pyflakes/mod.rs

@@ -133,6 +133,8 @@ mod tests {
     #[test_case(Rule::UndefinedName, Path::new("F821_15.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_16.py"))]
     #[test_case(Rule::UndefinedName, Path::new("F821_17.py"))]
+    #[test_case(Rule::UndefinedName, Path::new("F821_18.py"))]
+    #[test_case(Rule::UndefinedName, Path::new("F821_19.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_0.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_1.py"))]
     #[test_case(Rule::UndefinedExport, Path::new("F822_2.py"))]

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_18.py.snap

@@ -0,0 +1,4 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+

crates/ruff_linter/src/rules/pyflakes/snapshots/ruff_linter__rules__pyflakes__tests__F821_F821_19.py.snap

@@ -0,0 +1,12 @@
+---
+source: crates/ruff_linter/src/rules/pyflakes/mod.rs
+---
+F821_19.py:21:7: F821 Undefined name `y`
+   |
+19 | # Error: `y` is not defined.
+20 | x: (y := 1)
+21 | print(y)
+   |       ^ F821
+   |
+
+