Player physics improvements

[wjt]

This adds a few nice adjustments to the player controls:

• You get a few frames' grace after walking off a ledge where you can still jump ("coyote time")
• You get a few frames' grace if you press jump just before the character lands from a previous jump/fall ("jump buffering")
• You can control the height of the jump by releasing the jump key before the player reaches the top of the arc and starts descending ("jump cut")
• The player accelerates (over about 5 frames by default) when pressing or releasing left or right, rather than the velocity being set immediately. The acceleration can be controlled by the learner in the inspector.
• The player can now optionally double-jump.

I think this feels a bit nicer to play (though the jump is still a bit "floaty" for my liking). I would want learning team feedback on whether these tweaks are helpful or whether they complicate the example too much. They were fun to write though.

https://phabricator.endlessm.com/T35700

Screencast from 2024-10-25 14-47-16.webm

[wjt]

I made coyote time, jump buffering and jump cut configurable:

[manuq]

I gave it a try, it's impressive and moddable!

[wjt]

@jbourqueendless gave the thumbs-up to the concept on Slack so I'm undrafting this