Turn off mouse interaction in testbed

[rgov]

I'm not sure if it's possible to disable the mouse in the testbed. For example setting testbed.mouseForce = 0 triggers some other behavior rather than disabling it:

planck.js/testbed/StageTestbed.ts

Lines 243 to 249 in 4b6d6ec

	if (this.mouseForce) {
	targetBody = body;
	} else {
	mouseJoint = new MouseJoint({maxForce: 1000}, mouseGround, body, { x: point.x, y: point.y });
	world.createJoint(mouseJoint);
	}

The closest I can get is testbed.mouseForce = 0.001 which is not truly disabled and difficult to discover.