Auto merge of #23711 - saschanaz:frompoint, r=Manishearth

Implement DOMPoint.fromPoint

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Implements DOMPoint.fromPoint and fixes codegen to use default value when an optional dictionary member got `undefined`.

PS: The codegen change is about:

```webidl
dictionary MyDictionary {
  optional short myMember = 0;
  short anotherMember;
}

[Exposed=Window, Constructor]
interface MyInterface {
  void myMethod(optional MyDictionary myDict);
};
```

```js
// The following two must behave same
new MyInterface().myMethod({ myMember: undefined, anotherMember = 0 });
new MyInterface().myMethod({ anotherMember = 0 });
```

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23710

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- [x] There are tests for these changes

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components/script/dom/bindings/codegen/CodegenRust.py

@@ -6414,7 +6414,8 @@ class CGDictionary(CGThing):
         conversion = (
             "{\n"
             "    rooted!(in(cx) let mut rval = UndefinedValue());\n"
-            "    if r#try!(get_dictionary_property(cx, object.handle(), \"%s\", rval.handle_mut())) {\n"
+            "    if r#try!(get_dictionary_property(cx, object.handle(), \"%s\", rval.handle_mut()))"
+            " && !rval.is_undefined() {\n"
             "%s\n"
             "    } else {\n"
             "%s\n"