Make Transforms optional for Mesh3d, PointLight, Spotlight

## What problem does this solve or what need does it fill?

For Noumenal, I use a custom transform type, and use this type to set `GlobalTransform`. Forcing the `Transform` component causes a conflict with multiple systems writing to `GlobalTransform` in this case, and also wastes memory.

## What solution would you like?

I would like `Transform` components to be optional (not required.)

## What alternative(s) have you considered?

One workaround is to remove automatically added `Transform`s, but this is clunky, and I'm surprised that it even works.

## Additional context

With https://github.com/bevyengine/bevy/issues/16246, `Transform`s could be suggested components, or maybe there could be a way to remove or substitute required components when a plugin is loaded.