[red-knot] Do not show types for literal expressions on hover (#17290)

## Summary

Resolves #17289.

After this change, Red Knot will no longer show types on hover for
`None`, `...`, `True`, `False`, numbers, strings (but not f-strings),
and bytes literals.

## Test Plan

Unit tests.

crates/ruff_python_ast/src/nodes.rs

@@ -102,6 +102,19 @@ impl Expr {
 }
 
 impl ExprRef<'_> {
+    /// See [`Expr::is_literal_expr`].
+    pub fn is_literal_expr(&self) -> bool {
+        matches!(
+            self,
+            ExprRef::StringLiteral(_)
+                | ExprRef::BytesLiteral(_)
+                | ExprRef::NumberLiteral(_)
+                | ExprRef::BooleanLiteral(_)
+                | ExprRef::NoneLiteral(_)
+                | ExprRef::EllipsisLiteral(_)
+        )
+    }
+
     pub fn precedence(&self) -> OperatorPrecedence {
         OperatorPrecedence::from(self)
     }