Fix to behaviour of Pie menus where they don't release unless the mouse is moved first.

I believe this fits with the intended behavior:

Setting the tap timeout to 20 (default) or so will cause short taps (<20ms) to stick the pie menu open and anything longer to close the menu on key release.
Setting it to 1000 will make it act like it is now where a very long hold ( <10s) will still result in the pie menu sticking open.
Setting it to 0 will cause the pie menu to close no matter how short the key was tapped.

Re:
https://devtalk.blender.org/t/pie-menu-disable-on-release-key-patch/2237/27
https://developer.blender.org/T56949