Platformer player character

The Kid from IWBTG -style character. This requires a lot of things so it should be a nice guide for stuff to implement next.

We'll need:

[x] Lock rotation of a rigid body
- projection solution that feels kind of hacky but is actually equivalent to an angle constraint in XPBD
- maybe setting moment of inertia to infinite would be a better way to do this?
[x] Move with keyboard
[x] Jump
- [ ] only when on the ground
- requires events (#23) or some way to query this from the physics system on demand
- [ ] with customizable curve
- Exempt from world gravity or adding forces on top of it? Probably the latter because it allows to create environmental gravity effects that affect the player
[x] Shoot bullets
- Bullets should move linearly. Many ways to do this - kinematic body, dynamic body that doesn't respond to gravity, dynamic body restricted to a curve?
- Would be interesting if some gravity sources like point gravities in the world affected the bullets though, maybe a bitmask to decide which forcefields apply?
[x] Bullets disappear on contact with things
- See comment on jumping only when on the ground
[ ] Die on contact with specific objects
- Again, requires reacting to collisions, but also more associated information from the other thing (does it have component/tag x?)
- A great deal more logic is required to handle respawning; this can be worked out later when making an actual game
[ ] Sprites (#22)
[ ] Camera follows the player (related #6)

m0lentum / starframe