Optional ImageScaleMode

[ManevilleF]

Follow up to #11600 and #10588

@mockersf expressed some valid concerns about the current system this PR attempts to fix:

The ComputedTextureSlices reacts to asset change in both bevy_sprite and bevy_ui, meaning that if the ImageScaleMode is inserted by default in the bundles, we will iterate through most 2d items every time an asset is updated.

Solution

• ImageScaleMode only has two variants: Sliced and Tiled. I removed the Stretched default
• ImageScaleMode is no longer part of any bundle, but the relevant bundles explain that this additional component can be inserted

This way, the absence of ImageScaleMode means the image will be stretched, and its presence will include the entity to the various slicing systems

Optional components in bundles would make this more straigthfoward

Additional work

Should I add new bundles with the ImageScaleMode component ?

[ManevilleF]

@mockersf does this adress your concerns ? @alice-i-cecile what do you think of this "extra component" concept ?

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Could you add some context on what users should update when this change get released in a new version of Bevy?
It will be used to help writing the migration guide for the version. Putting it after a ## Migration Guide will help it get automatically picked up by our tooling.

[alice-i-cecile]

I like the additional component: this feels very much like how the ECS architecture is supposed to work. I think you did an excellent job documenting the fact that this exists as well.

[pablo-lua]

I think that's a fair change on this field and can rather improve perf when we don't need this feature, so all good

[pablo-lua]

Should I add new bundles with the ImageScaleMode component?

IMO no, the docs about this feature is good enough, the user can pretty much find this on they own, and we even have examples showing how to use this