Add support for supplying thisObj

Jint.Tests/Runtime/FunctionTests.cs

@@ -193,5 +193,16 @@ public void CanInvokeFunctionViaEngineInstance()
             Assert.Equal(123, engine.Call(function, 123));
             Assert.Equal(123, engine.Call("bar", 123));
         }
+
+        [Fact]
+        public void CanInvokeFunctionViaEngineInstanceWithCustomThisObj()
+        {
+            var engine = new Engine();
+
+            var function = engine.Evaluate("function baz() { return this; }; baz;");
+
+            Assert.Equal("I'm this!", TypeConverter.ToString(engine.Call(function, "I'm this!", Arguments.Empty)));
+            Assert.Equal("I'm this!", TypeConverter.ToString(function.Call("I'm this!", Arguments.Empty)));
+        }
     }
 }

Jint/Engine.cs

@@ -1245,7 +1245,7 @@ public JsValue Call(JsValue callable, params JsValue[] arguments)
         /// <param name="thisObject">Value bound as this.</param>
         /// <param name="arguments">The arguments of the call.</param>
         /// <returns>The value returned by the call.</returns>
-        private JsValue Call(JsValue callable, JsValue thisObject, params JsValue[] arguments)
+        public JsValue Call(JsValue callable, JsValue thisObject, JsValue[] arguments)
         {
             JsValue Callback()
             {

Jint/JsValueExtensions.cs

@@ -443,6 +443,19 @@ public static JsValue Call(this JsValue value, params JsValue[] arguments)
             return objectInstance.Engine.Call(value, arguments);
         }
 
+        [Pure]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static JsValue Call(this JsValue value, JsValue thisObj, params JsValue[] arguments)
+        {
+            if (value is not ObjectInstance objectInstance)
+            {
+                ExceptionHelper.ThrowArgumentException(value + " is not object");
+                return null;
+            }
+
+            return objectInstance.Engine.Call(value, thisObj, arguments);
+        }
+
         /// <summary>
         /// If the value is a Promise
         ///     1. If "Fulfilled" returns the value it was fulfilled with