Number of DPad in controls

Property definitions

gamnit $ VirtualGamepad :: n_dpads
	# Number of `DPad` in `controls`
	private fun n_dpads: Int
	do
		var n_dpads = 0
		for c in controls do if c isa DPad then n_dpads += 1
		return n_dpads
	end
lib/gamnit/virtual_gamepad/virtual_gamepad.nit:123,2--129,4