Consistently use pressed / released terminology in `bevy_picking`

[alice-i-cecile]

should these be called pressed and released instead of down and up to match the methods on ButtonInput? https://dev-docs.bevyengine.org/bevy/input/struct.ButtonInput.html#method.just_pressed

If we're doing this, it should be a global concept rename (ex: Pointer<Down> and Pointer<Up> types, all of the methods)

Originally posted by @cart in https://github.com/bevyengine/bevy/issues/16176#issuecomment-2448311264

[viridia]

I would argue against this, although I could be convinced otherwise. "up" and "down" are used widely in HTML events and their meanings are unambiguous. Generally, I use the words "up" and "down" when I want to talk about events, and "pressed" when I am talking about states.

[cart]

Given that just_pressed is literally capturing the same concept as Pointer<Down>, it seems odd to me to use different terminology. Consistency here seems desirable.