Fix onboarding background - Canvas: trying to draw too large bitmap

[bemusementpark]

Task/Issue URL: #3914

Description

We were calling View#setBackground which is incorrect and inefficient because:

android:scaleType="centerCrop" applies to src of the ImageView, not the background of a View, which is set in WelcomePage

I could've changed this to setImageResource, but we can just set src in xml, and add xml resources for light and night

This should fix the OOM, because setting the background probably set an upscaled version of this bitmap, so even though the large version of the bitmap is about 10MB, this device perhaps thinks it is an xxhdpi device and does an x3 making this large bitmap require 100MB. That's probably what we see in the logs anyway. This PR will hopefully scale the bitmap properly so Canvas is not overwhelmed.

I've simplified the bitmap resolution by using the resource folders for each bitmap for each combination of light | dark & < 600dp | > 600dp. I just deleted the holder drawable files, because the only interesting thing they did was set clampMode, but that wasn't (intentionally) being used anyway, because the bitmap was usual too big, and if it was going to be used it probably wouldn't look very good depending on which edge is clamped. And there was a scaleMode set on the ImageView which was unused because no src was applied.

I also changed sceneBg to ImageView in one override to match the other xml file, so that the binding will not be "downcast" to a View, but will be accessible as ImageView, which should help devs find the ImageView methods they need, and remove any desire for casting.

If anyone doesn't know, <ImageView> will be inflated as AppCompatImageView if inflated in an AppCompatActivity.

Steps to test this PR

Open the app in a low spec tablet.
Observe app does not crash.

UI changes

Before	After
!()	()
!()	(![Screenshot 2024-08-11 at 9 14 15 PM]())

...and the proper center-cropping kinda looks better too 🎉