The `bevy_render::camera::camera` module shares its name with its parent module

[LikeLakers2]

While working on #17194, I came across bevy_render::camera::camera, which was linting clippy::module_inception.

While I did put in a placeholder reason explaining the difference, I believe either bevy_render::camera or bevy_render::camera::camera should be renamed, as the current naming is confusing.

My suggestion would be to rename bevy_render::camera to bevy_render::viewport, as it appears to contain viewport-related stuff as a whole; compared to bevy_render::camera::camera which only relates to the Camera component.

[LikeLakers2]

@BenjaminBrienen Actually, I wouldn't mark this as ready for implementation.

When I brought this up in #rendering-dev in the Discord, it appears there was some contention about my suggested name; so perhaps it may be wise to have some discussion first?

[IceSentry]

Personally, I'd prefer to not touch it and wait for the bevy_camera refactor that was planned to pull it out of bevy_render.

If we absolutely need to deal with this now, my suggestion would be to move the Camera struct to mod.rs and move the Viewport and Exposure stuff to separate files.