Previously, when an element is created, it's added to the scene and updated with informMutation, leading to an increase/change in scene version. This means that StaticCanvas, which gets re-rendered as the scene version updates, re-renders on every update happening to the new element. Given a large enough scene, we would see significant lags. And for elements like free draws, this kind of lag is perceived poorly.

This PR improves the drawing of new elements by

• while a new element is still added to the elements array / scene, updating it does not trigger scene version change (so static canvas is not re-rendered);
• and so to have the new element that's being created drawn, a canvas dedicated to the drawing of a new element is added

Implementation wise, building on the previous draggingElement -> newElement refactor, we have

• newElement points to a new (non-selection) element that's being created
• editingElement gets renamed to editingTextElement and is only used for a text that's being created/edited
• when the creation of a new element is over (or when necessary), we reset states so that newElement is null and trigger scene updates so that the newly created element is rendered on the static canvas instead

Right now, this new element drawing improvement is only in the single player mode. Whether we should bring this feature over to collaboration mode remains to be seen.