Make axis strength always be positive

[johanhelsing]

Since an analog stick is split into four different inputs (i.e. negative x) it made more sense to me that the strength should always go from 0 to 1 regardless of which of the four directions it is.

How I use it in my own code:

pub trait AxisInput {
    fn horizontal(&self) -> f32;
}

impl AxisInput for InputMap<Action> {
    fn horizontal(&self) -> f32 {
        -self.strength(Action::Left) + self.strength(Action::Right)
    }
}

pub fn read_inputs(mut query: Query<&mut Player>, input_map: Res<InputMap<Action>>) {
    let horizontal = input_map.horizontal();
    // ...
}