Always teleport full distance, even with analogue stick input

[wjt]

_teleport() takes an input_direction in range [-1, 1] as input, and if it is not approximately zero, teleports the player by input_direction * TELEPORT_DISTANCE.

The direction comes from:

var direction = Input.get_axis(Actions.lookup(player, "left"), Actions.lookup(player, "right"))

When using keyboard or D-pad input, this is always -1, 0, or 1. But with an analogue joystick it can be any value between -1 and 1. (Actually strictly speaking it can be [-1.0, -0.5], 0, or [0.5, 1.0] because the left/right actions' dead zones are set to 0.5.)

Use signf to round any negative value to -1 and any positive value to 1 when calculating how far to teleport the player.

[wjt]

Eagle-eyed viewers on today's Loom Lounge may have spotted me discovering and fixing this bug.

@jgbourque I think this is obscure enough that we shouldn't leave it as a bug for learners to find & potentially exploit?

[github-actions]

Play this branch at https://endlessm.github.io/moddable-platformer/branches/endlessm/wjt/teleport-distance-signf/.

(This launches the game from the start, not directly at the change(s) in this pull request.)

[wjt]

I pushed a second version that adds a huge comment explaining what signf() does. But I think this detracts from the simplicity of the function...