[3.x] Physics Interpolation - Fix behavior on pause

[lawnjelly]

Resets nodes on pause, which prevents them pausing in a glitchy state (where prev and current transforms are different, and no longer being updated).

Fixes #92391 (comment)

Notes

• This may not fix every scenario for pausing, but should fix the major ones.
• It is possible skinned 2D might need a tweak or any other manually interpolated nodes, but will wait for MRP.

[Calinou]

Tested locally on Truck Town (with a pause toggle key added), it works as expected.

Note that this introduces a visible hitch when pausing, although this is hard to notice at 60 Hz physics – even at 30 Hz, it's not that obvious. On the bright side, this has the benefit of showing you the "true" state of the game whenever you pause, which can be valuable for some use cases (such as frame-by-frame advance).

In this 120 FPS video, I spam the pause key while driving:

pause_10hz.mp4

Curiously, if you set get_tree().paused = true then false within the same frame, this will reset interpolation on everything without pausing the game:

pause_then_unpause_10hz.mp4

[lawnjelly]

Regarding the glitch, it is possible we can later look into having both a paused interpolation fraction and a running interpolation fraction, but this should hopefully deal with the major problem of paused nodes continuously interpolating between different prev and curr transforms, so should be quite serviceable for the meantime.

[lawnjelly]

Thanks!