Move SVG overlay and floating toolbar out of r3fRoot

[axelboc]

#1467 allows further simplification:

• svgOverlay can be rendered directly into canvasWrapper instead of r3fRoot. This opens up an opportunity to let SVG elements overflow in the future; however, for now, the overflow remains hidden. It also removes the need to render the overlay with Html, which most likely provides a very small performance gain on initial render.
• floatingToolbar can be rendered into visCanvas and positioned with CSS Grid properties. This paves the way to Event propagation to canvas #1388 (comment) and also removes the need for Html.

[axelboc]

/approve

[loichuder]

Great !