Snap time panel size to full screen and collapsed states

[abey79]

The time panel height is currently clamped to hard-coded values to avoid visual glitches (#3169). There is usefulness to have the time panel span the entire screen. Likewise, it would be nice to be able to get to the collapsed state of the time panel by reducing its size. This would further enable to free the top-right button to actually fully hide the time panel, which is currently not possible.

To achieve this, some "snapping" mechanism should be used/built (possibly in egui) and used to avoid drawing the viewport/side panels with very small heights (its either some acceptable minimum, or not at all and the time panel is full screen).

Supersedes #3169