LibJS: Update NumberPrototype's this_number_value() to take a Value

This is now about as close to the spec as it gets - instead of querying
the |this| value inside of the function, we now pass it in from the
outside.
Also get rid of the oddly specific error messages, they're nice but
pretty inconsistent with most others. Let's prefer consistency and
simplicity for now.

Other than that, no functionality change.

Userland/Libraries/LibJS/Runtime/ErrorTypes.h

@@ -54,7 +54,6 @@
     M(NotASymbol, "{} is not a symbol")                                                                                                 \
     M(NotIterable, "{} is not iterable")                                                                                                \
     M(NotObjectCoercible, "{} cannot be converted to an object")                                                                        \
-    M(NumberIncompatibleThis, "Number.prototype.{}() called with incompatible this target")                                             \
     M(ObjectDefinePropertyReturnedFalse, "Object's [[DefineProperty]] method returned false")                                           \
     M(ObjectFreezeFailed, "Could not freeze object")                                                                                    \
     M(ObjectSealFailed, "Could not seal object")                                                                                        \

Userland/Libraries/LibJS/Runtime/NumberPrototype.cpp

@@ -42,22 +42,21 @@ NumberPrototype::~NumberPrototype()
 {
 }
 
-// https://tc39.es/ecma262/#thisnumbervalue
+// thisNumberValue, https://tc39.es/ecma262/#thisnumbervalue
-static Value this_number_value(GlobalObject& global_object, StringView const& name)
+static Value this_number_value(GlobalObject& global_object, Value value)
 {
+    if (value.is_number())
+        return value;
+    if (value.is_object() && is<NumberObject>(value.as_object()))
+        return static_cast<NumberObject&>(value.as_object()).value_of();
     auto& vm = global_object.vm();
-    auto this_value = vm.this_value(global_object);
+    vm.throw_exception<TypeError>(global_object, ErrorType::NotA, "Number");
-    if (this_value.is_number())
-        return this_value;
-    if (this_value.is_object() && is<NumberObject>(this_value.as_object()))
-        return static_cast<NumberObject&>(this_value.as_object()).value_of();
-    vm.throw_exception<TypeError>(global_object, ErrorType::NumberIncompatibleThis, name);
     return {};
 }
 
 JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_string)
 {
-    auto number_value = this_number_value(global_object, "toString");
+    auto number_value = this_number_value(global_object, vm.this_value(global_object));
     if (vm.exception())
         return {};
 
@@ -134,7 +133,7 @@ JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::to_string)
 
 JS_DEFINE_NATIVE_FUNCTION(NumberPrototype::value_of)
 {
-    return this_number_value(global_object, "valueOf");
+    return this_number_value(global_object, vm.this_value(global_object));
 }
 
 }

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.toString.js

@@ -77,7 +77,7 @@ test("errors", () => {
         [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
             expect(() => Number.prototype.toString.call(value)).toThrowWithMessage(
                 TypeError,
-                "Number.prototype.toString() called with incompatible this target"
+                "Not a Number object"
             );
         });
     });

Userland/Libraries/LibJS/Tests/builtins/Number/Number.prototype.valueOf.js

@@ -14,7 +14,7 @@ test("errors", () => {
         [true, [], {}, Symbol("foo"), "bar", 1n].forEach(value => {
             expect(() => Number.prototype.valueOf.call(value)).toThrowWithMessage(
                 TypeError,
-                "Number.prototype.valueOf() called with incompatible this target"
+                "Not a Number object"
             );
         });
     });