Remove the Component trait implementation from Handle

[tim-blackbird]

Objective

• Closes Remove Component trait impl from Handle<T> #15716
• Closes Stop using Handle<MeshletMesh> as a component #15718

Solution

• Replace Handle<MeshletMesh> with a new MeshletMesh3d component
• As expected there were some random things that needed fixing:
  • A couple tests were storing handles just to prevent them from being dropped I believe, which seems to have been unnecessary in some.
  • The SpriteBundle still had a Handle<Image> field. I've removed this.
  • Tests in bevy_sprite incorrectly added a Handle<Image> field outside of the Sprite component.
  • A few examples were still inserting Handles, switched those to their corresponding wrappers.
  • 2 examples that were still querying for Handle<Image> were changed to query Sprite

Testing

• I've verified that the changed examples work now

Migration Guide

Handle can no longer be used as a Component. All existing Bevy types using this pattern have been wrapped in their own semantically meaningful type. You should do the same for any custom Handle components your project needs.

The Handle<MeshletMesh> component is now MeshletMesh3d.

The WithMeshletMesh type alias has been removed. Use With<MeshletMesh3d> instead.

[alice-i-cecile]

I've extended the migration guide for you :)

[JMS55]

Thanks for doing this! Small nit, can we remove the WithMeshletMesh type alias? I never liked it to begin with, and it's not even that complex now that handle is gone. Feels uneeded.