Migrate anisotropy to feathers

[tevans-3]

Objective

Addresses one part of #25032

Solution

• Switch the 3d/anisotropy.rs example to use Feathers checkboxes and radios
• Refactor the checkbox helper to accept an "IsChecked" flag and spawn both checked and unchecked variants (the previous version only let callers create unchecked boxes; I think this caused some mild awkwardness for Migrate bloom_2d to use Feathers. #25431).
• The checkbox refactor was necessary here because anisotropy is turned on by default, but the previous helper only allowed callers to create unchecked boxes, so to a user it looked like anisotropy was toggled off even though it was actually on
• Updated the other users of checkbox.rs (2d_shapes.rs and the pending Migrate 3d_shapes to feathers #25436) to pass IsChecked to the helper

Because the checkbox refactor touches #25436, that PR blocks this one.

Testing

cargo run --example anisotropy --features="bevy_feathers jpeg pbr_anisotropy_texture"

I also tested the other callers of feathers_option_checkbox and verified that they still work with the refactor.

anisotropy.mp4

[tevans-3]

the current CI failure is fixed by #25492