[ENHANCEMENT/BUGFIX] Bopper sync and bpm change events

[MidyGamy]

This fixes the bopper desyncing from each other, imitating the if(curBeat % 2 == 0) dad.dance(); from the 0.3.X of the game, but calculate it automatically with the actual idle animation duration, using danceEvery as a well, making it consistent with the BPM and camera bopping.

For it to work, I also included onBpmChange() and the bpmChange SongTimeScriptEvent, called every time the bpm changes, allowing easier scripting instead of manually detecting it though beatHit if we use an .hxc script.

To do:
Find a way to handle the automation for a decimal danceEvery, currently ignored and works like before

[MidyGamy]

Btw, this is a rewrite of #3092, which was broken and unorganized

[MidyGamy]

Ok I might found a solution, but maybe a better looking one could be found?
(P.S. I don't even understand why decimal danceEvery is even a thing...)

[AbnormalPoof]

(P.S. I don't even understand why decimal danceEvery is even a thing...)

#2925 (comment):

I will also change danceEvery so that it uses event.step % (danceEvery * STEPS_PER_BEAT) so it works with any multiple of 0.25

[MidyGamy]

(P.S. I don't even understand why decimal danceEvery is even a thing...)

#2925 (comment):

I will also change danceEvery so that it uses event.step % (danceEvery * STEPS_PER_BEAT) so it works with any multiple of 0.25

Yeah... still confused...