Do not enforce that layers with invalid bounds are not focusable

This is a partial revert of ag/16743825.

We previously made this change to expect more strict preconditions for
input windows, but are now running into app-compat issues.

Since it is not essential, we no longer enforce that layers with invalid
bounds are not focusable.

Bug: 225029938
Test: atest libgui_test
Test: manual with affected apps
Change-Id: Ic70eebf991322adc93bd824528d8d87f892d01e1