main.DomAccess: getBoundingClientRect() does not pass minHeight & minWidth to the app worker

the json conversion works (had to add new class fields for it):

we should keep this change.

however, there is a lot more to it. in case we are creating a worker message, we now get the 2 missing values while creating it:

but, the result inside the app worker will convert the result back into DOMRect instances (native code), in which case we lose the custom fields right away:

not sure, if we can even manipulate this part. might(!) be possible.

testing it in firefox => messages containing DOMRects feel slow.

@ExtAnimal: before doing a final change, we should sync on this ticket. my current recommendation is that getBoundingClientRect() inside main.DomAccess should just return a plain object (we can use the new toJSON() method for it) and other non-remote methods could convert it to Rectangle instances.