LibJS: Reset in_formal_parameter_context after entering a new function

Fixes a bug when "'Await' expression is not allowed in formal parameters
of an async function" is thrown for "await" encountered in a function
definition assigned to a default function parameter.

Fixes loading of https://excalidraw.com/

Userland/Libraries/LibJS/Parser.cpp

@@ -982,6 +982,8 @@ static bool is_simple_parameter_list(Vector<FunctionParameter> const& parameters
 
 RefPtr<FunctionExpression const> Parser::try_parse_arrow_function_expression(bool expect_parens, bool is_async)
 {
+    TemporaryChange in_formal_parameter_context_rollback(m_state.in_formal_parameter_context, false);
+
     if (is_async)
         VERIFY(match(TokenType::Async));
 
@@ -2888,6 +2890,7 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u16 parse_options, O
     TemporaryChange continue_context_rollback(m_state.in_continue_context, false);
     TemporaryChange class_field_initializer_rollback(m_state.in_class_field_initializer, false);
     TemporaryChange might_need_arguments_object_rollback(m_state.function_might_need_arguments_object, false);
+    TemporaryChange in_formal_parameter_context_rollback(m_state.in_formal_parameter_context, false);
 
     constexpr auto is_function_expression = IsSame<FunctionNodeType, FunctionExpression>;
     FunctionKind function_kind;

Userland/Libraries/LibJS/Tests/regress/allow-await-in-a-func-def-assigned-to-default-param.js

@@ -0,0 +1,23 @@
+test('Do not throw syntax error when "await" is used in an arrow function definition assigned to a default function parameter', async () => {
+    async function f(
+        g = async () => {
+            await 1;
+        }
+    ) {
+        return await g();
+    }
+
+    expect(await f()).toBe(1);
+});
+
+test('Do not throw syntax error when "await" is used in a function definition assigned to a default function parameter', async () => {
+    async function f(
+        g = async function () {
+            await 1;
+        }
+    ) {
+        return await g();
+    }
+
+    expect(await f()).toBe(1);
+});