[JSC] Refine SyntaxError message for generator method parsing failure

https://bugs.webkit.org/show_bug.cgi?id=264368
<rdar://problem/118081884>

Reviewed by Justin Michaud.

This change rewords SyntaxError message, thrown in case of generator method parsing failure,
to mention "method" rather than "function", aligning error wording for sync generator functions
with async counterparts.

Also, tweaks the helper to return "generator function" instead of "generator" for GeneratorBodyMode,
which is unobservable yet matches the terminology of the spec [1].

[1]: https://tc39.es/ecma262/#sec-generator-objects

* JSTests/stress/generator-class-methods-syntax.js:
* JSTests/stress/regress-189292.js:
* Source/JavaScriptCore/parser/Parser.cpp:
(JSC::stringForFunctionMode):

Canonical link: https://commits.webkit.org/270379@main

JSTests/stress/generator-class-methods-syntax.js

@@ -27,7 +27,7 @@ class Cocoa {
     {
     }
 }
-`, `SyntaxError: Cannot declare a generator function named 'constructor'.`);
+`, `SyntaxError: Cannot declare a generator method named 'constructor'.`);
 
 testSyntax(`
 class Cocoa {

JSTests/stress/regress-189292.js

@@ -14,5 +14,5 @@ function test(script) {
 }
 
 assert(test("class C1 { async constructor() { } }"), "SyntaxError: Cannot declare an async method named 'constructor'.");
-assert(test("class C1 { *constructor() { } }"), "SyntaxError: Cannot declare a generator function named 'constructor'.");
+assert(test("class C1 { *constructor() { } }"), "SyntaxError: Cannot declare a generator method named 'constructor'.");
 assert(test("class C1 { async *constructor() { } }"), "SyntaxError: Cannot declare an async generator method named 'constructor'.");

Source/JavaScriptCore/parser/Parser.cpp

@@ -2265,11 +2265,11 @@ static const char* stringForFunctionMode(SourceParseMode mode)
         return "function";
     case SourceParseMode::MethodMode:
         return "method";
-    case SourceParseMode::GeneratorBodyMode:
-        return "generator";
     case SourceParseMode::GeneratorWrapperFunctionMode:
-    case SourceParseMode::GeneratorWrapperMethodMode:
+    case SourceParseMode::GeneratorBodyMode:
         return "generator function";
+    case SourceParseMode::GeneratorWrapperMethodMode:
+        return "generator method";
     case SourceParseMode::ArrowFunctionMode:
         return "arrow function";
     case SourceParseMode::AsyncFunctionMode: