SpriteFramesEditor Fix preview grid in "Select Frames" dialog

[kleonc]

Fixes #52099 (I'll probably enhance this dialog in another PR, this one is bugfix only).
Fixes #52745.
Cherry-pickable 3.x, 3.3.

Makes grid being drawn according to the frames this dialog outputs (it allows integer-only frame sizes), scaling/zooming wasn't properly taken into account. Input handling is changed accordingly too. Output frames are unchanged, the preview was broken.

Example:

so the frame size is (64, 64) / (13, 11) = (4, 5)

3.4.beta4:	this PR (against 3.x):

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 3.4.

[akien-mga]

Cherry-picked for 3.3.4.

Edit: Undid cherry-pick as it's too much hassle to include all other commits which were needed for this to work, and I don't have bandwidth to actually test that it doesn't regress.

[akien-mga]

So it's actually too much hassle to backport this fix to 3.3 as it depends on 3 previous PRs which also need to be backported, and the sum of those seem a bit too feature-packed for 3.3 IMO: #47802, #48977, #51031.

I would suggest making a dedicated PR for 3.3 with relevant fixes if need be, or we leave it at 3.4.