Add "init" lifecycle hook

[quinton-ashley]

Added two lines of code that implement the "init" lifecycle hook in p5 v2.

This is needed for preload system compatibility. Issue #7742 can't be fixed by moving the current "presetup" hook.

[davepagurek]

Hey @quinton-ashley, thanks for making a PR! I think because we aren't awaiting the hooks, there are some bugs currently. Since we currently await every lifecycle hook, if there exists more than one addon using init, it looks like only the first one gets run before globals are initialized: https://editor.p5js.org/davepagurek/sketches/zZy1xer18

Arguably we shouldn't be awaiting non-async hooks though -- see some discussion here: #7770 (comment) If we end up implementing that, then this implementation will work as-is though (assuming init hooks are never async, which I think is reasonable if this is intended only to be used to initialize globals.)

[quinton-ashley]

@davepagurek ah yes you're right

assuming init hooks are never async, which I think is reasonable if this is intended only to be used to initialize globals.

Yes and for now I'll edit the PR based on that assumption.

[quinton-ashley]

I think this PR works as a fix for #7742 now.

I'd like if it could be merged before other lifecycle changes are finalized, as that could take a while.