Feature Request: improved diagnostics overlay tools

An extension of https://github.com/bevyengine/bevy/issues/25018 to make the diagnostic tools more helpful.

- Make the interaction opt-in or able to be turned off (window moving, window drop down toggling). Its a cool thing to have but my game is first person without a cursor so I can't move them normally and instead i just keep accidentally moving them with my invisible cursor and being unable to move them back. Additionally its just wasted cycles in update if I don't want to move them.

- Add more FPS content. Especially a low frame stat to the FPS window so I can detect frame stutters. iyes_perf_ui had this and it was very helpful. I know I can probably manually implement this as a custom window but at least give me the frame drop stat and frame time in miliseconds in the default FPS window :)
https://github.com/IyesGames/iyes_perf_ui

- An example in the bevy examples page cause im having a hard time using this but it has great potential.

- Hard coding the initial position is kinda just wrong. It causes all of the windows to spawn in the same place and again I cant move them in my cursorless game. ```const INITIAL_OFFSET: Val = Val::Px(32.);```

Start by reviewing issue #25018 and the current diagnostics overlay, then compare the requested FPS metrics with iyes_perf_ui. Scope the opt-in interaction, frame-time and low-FPS display, example, and non-overlapping initial positions; done means these requested behaviors are implemented and usable without a cursor.

Written by the indexing model from the issue text.