Change "playfield" skin layer to respect shifting playfield border in osu! ruleset

[peppy]

As touched on in #28579. I personally think this makes sense.

Before	After

[bdach]

Conceptually seems fine, my only worry would be that this is going to affect existing skins. In worst cases it can make elements go off-screen entirely. Not sure whether that can be avoided in any sane way, though...

[april83c]

my only worry would be that this is going to affect existing skins. In worst cases it can make elements go off-screen entirely.

Can confirm my skin is affected by this (elements off-screen at the bottom):

And what it's supposed to look like:

I don't like this change because, for my elements to be visible at low circle size (big circles), I have to move my elements really far in, but then on higher circle size (small circles) they feel like they're too close. But also, my skin is really unconventional and the new behavior is probably better for most skins.

It would be nice if both behaviors were available (new one by default but have some way to use the old one), but I have no idea what the UX for that would be (option in skin config/ini? make both available as separate layers? some other way of doing it if anchor point locations get detached from layers?)

Or maybe I should just rethink my skin... it really isn't that big of a deal

(Also another thing to consider: I don't like that updates can break skins; didn't stable have a skin version parameter to keep compatibility with skins made on older versions?)

[peppy]

(Also another thing to consider: I don't like that updates can break skins; didn't stable have a skin version parameter to keep compatibility with skins made on older versions?)

We do our best to avoid this. But sometimes the overhead is not worth it.