`bevy_sprite` picking backend does not honor render layers

## Bevy version

0.15

## What you did

Create multiple sprites, multiple cameras, selectively render some of the sprites in some of the cameras using render layers. Use `bevy_picking`.

## What went wrong

Sprites are picked across all cameras (that have the window as a render target) regardless of render layers.

---

(Also, if #16886 is merged, this should probably also apply to that.)

Start in the bevy_sprite picking backend and trace how sprites are selected across cameras with window render targets. Reproduce the multiple-camera, multiple-render-layer case described in the issue, and verify that picking only considers sprites visible through the applicable render layers; also check whether the behavior described by #16886 needs the same treatment.

Written by the indexing model from the issue text.