feat: Implement InputMapper

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

==================

This PR implements a new input mapper for excalibur which is useful for mapping multiple input sources into specific commands. This can be used to enable accessibility for your users adding ways for them to provide different inputs!

This examples shows how to map multiple types of input for the same action!

const moveRight = (amount: number) => { actor.vel.x = 100 * amount }
const moveLeft = (amount: number) => { actor.vel.x = -100 * amount }
const moveUp = (amount: number) => { actor.vel.y = -100 * amount }
const moveDown = (amount: number) => { actor.vel.y = 100 * amount }
engine.inputMapper.on(({keyboard}) => keyboard.isHeld(ex.Keys.ArrowRight) ? 1 : 0, moveRight);
engine.inputMapper.on(({gamepads}) => gamepads.at(0).isButtonPressed(ex.Buttons.DpadRight) ? 1 : 0, moveRight);
engine.inputMapper.on(({gamepads}) => gamepads.at(0).getAxes(ex.Axes.LeftStickX) > 0 ? gamepads.at(0).getAxes(ex.Axes.LeftStickX) : 0, moveRight);