feat: Backdrop (static backgrounds) component for CameraComponent

[spydon]

Description

This PR adds a backdrop component to the CameraComponent which renders behind the world.
With this change the rendering order looks like this:

backdrop
world
viewport
viewfinder

In the following example you can see a ParallaxComponent attached to the backdrop, a player and some other components attached to the world, and some texts attached to the viewfinder and viewport:

Checklist

• I have followed the Contributor Guide when preparing my PR.
• I have updated/added tests for ALL new/updated/fixed functionality.
• I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• I have updated/added relevant examples in examples or docs.

Breaking Change?

• Yes, this PR is a breaking change. (Very minor, because not many add components to the viewfinder)

Migration instructions

If you were previously adding your HUDs directly to the viewfinder, add them to the viewport instead.

Related Issues

[ufrshubham]

@spydon, just a thought, what if let viewfinder + viewport both render on top of the world and use a separate parent for the background? Something like a world background component?

Just thinking in terms of a real-life camera, where UI elements of viewfinder are always displayed on top of the image that is being captured.

[spydon]

@spydon, just a thought, what if let viewfinder + viewport both render on top of the world and use a separate parent for the background? Something like a world background component?

Just thinking in terms of a real-life camera, where UI elements of viewfinder are always displayed on top of the image that is being captured.

Yeah, that might make more sense. Do you think the viewfinder should be affected by the transformations or not then?

[ufrshubham]

Do you think the viewfinder should be affected by the transformations or not then?

Making it behave similar to viewport should be fine I think.

[spydon]

@ufrshubham what do you think about this solution? :)

[ufrshubham]

Looks perfect! (until someone says otherwise 😉)