LibJS: Handle symbol PropertyName in primitive assignment error

We can't just to_string() the PropertyName, it might be a symbol.
Instead to_value() it and then use to_string_without_side_effects() as
usual.

Fixes #4062.

Libraries/LibJS/Tests/strict-mode-errors.js

@@ -5,5 +5,8 @@ test("basic functionality", () => {
         expect(() => {
             primitive.foo = "bar";
         }).toThrowWithMessage(TypeError, "Cannot assign property foo to primitive value");
+        expect(() => {
+            primitive[Symbol.hasInstance] = 123;
+        }).toThrowWithMessage(TypeError, "Cannot assign property Symbol(Symbol.hasInstance) to primitive value");
     });
 });