RN Button size changes when in press state

[acoates-ms]

When you click on a RN button, the size of the button shrinks slightly, causing content below it to shift which is distracting.
(This can be seen clearly in the RN Gallery app)

[chrisglein]

There's a bottom border on the control that is displayed when idle:

But not when pressed:

Which is correct... but shouldn't affect the layout size.

Since this is in the JS button, in the platform override of Button.js, this affects Paper and Fabric.

Simplest fix to try: keep the border but make transparent color.