[Scene] Add blur parameters to rects

[ErikReider]

No description provided.

[WillPower3309]

Hmm, it's really too bad blur is reliant on the texture discarding :/ if blur was a node we wouldn't need this! Maybe we can separate blur into a node and get the tex stencil of the buffer above it similar to what we do for the borders and shadows

[WillPower3309]

Oops deleted my comment accidentally, tldr was we should make blur a node and then get the tex stencil similar to how we get the rect / buffer dimensions of the above node for shadows and borders

[WillPower3309]

Then we not only simplify our rendering logic but also get this for free!

[WillPower3309]

Also, we don't need this for swayfx compat. We can think about moving to a blur node after we rebase swayfx :)