[red-knot] Infer boolean literal expression (#12688)

## Summary

This PR implements type inference for boolean literal expressions.

## Test Plan

Add test cases for `True` and `False`.

crates/red_knot_python_semantic/src/types.rs

@@ -130,6 +130,8 @@ pub enum Type<'db> {
     Union(UnionType<'db>),
     Intersection(IntersectionType<'db>),
     IntLiteral(i64),
+    /// A boolean literal, either `True` or `False`.
+    BooleanLiteral(bool),
     // TODO protocols, callable types, overloads, generics, type vars
 }
 
@@ -175,6 +177,7 @@ impl<'db> Type<'db> {
                 // TODO raise error
                 Type::Unknown
             }
+            Type::BooleanLiteral(_) => Type::Unknown,
         }
     }
 }

crates/red_knot_python_semantic/src/types/display.rs

@@ -35,6 +35,9 @@ impl Display for DisplayType<'_> {
             Type::Union(union) => union.display(self.db).fmt(f),
             Type::Intersection(intersection) => intersection.display(self.db).fmt(f),
             Type::IntLiteral(n) => write!(f, "Literal[{n}]"),
+            Type::BooleanLiteral(boolean) => {
+                write!(f, "Literal[{}]", if *boolean { "True" } else { "False" })
+            }
         }
     }
 }

crates/red_knot_python_semantic/src/types/infer.rs

@@ -939,12 +939,10 @@ impl<'db> TypeInferenceBuilder<'db> {
     }
 
     #[allow(clippy::unused_self)]
-    fn infer_boolean_literal_expression(
-        &mut self,
-        _literal: &ast::ExprBooleanLiteral,
-    ) -> Type<'db> {
-        // TODO builtins.bool and boolean Literal types
-        Type::Unknown
+    fn infer_boolean_literal_expression(&mut self, literal: &ast::ExprBooleanLiteral) -> Type<'db> {
+        let ast::ExprBooleanLiteral { range: _, value } = literal;
+
+        Type::BooleanLiteral(*value)
     }
 
     #[allow(clippy::unused_self)]
@@ -1649,6 +1647,18 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn boolean_literal() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_file("src/a.py", "x = True\ny = False")?;
+
+        assert_public_ty(&db, "src/a.py", "x", "Literal[True]");
+        assert_public_ty(&db, "src/a.py", "y", "Literal[False]");
+
+        Ok(())
+    }
+
     #[test]
     fn resolve_union() -> anyhow::Result<()> {
         let mut db = setup_db();