Provide a way to refresh native field bounds globally and implement for ios.

Ideally, this would magically update anytime the screen bounds of a Field changes, but that's
pretty complicated. So instead, allow applications to force a global update when it is known
that something is changing, such as sliding a root layer.
Also support refreshing native overlay bounds on SWT.

After some testing on Linux, SWT generates a lot of artifacts if fields are moved around directly,
so post a pending refresh repeatedly to invokeLater until some time has passed.