Ignore unneeded soft keyboard in ACTV height calc

Before, if dropDownAlwaysVisible was false,
the soft keyboard height was always taken into
account when calculating the available vertical space for
the AutoCompleteTextView drop-down height.
This meant that the drop-down would never pop over the soft
keyboard when navigating in the drop-down list.

This change makes the drop-down pop over the soft keyboard
when the keyboard is not needed, regardless of the value of
dropDownAlwaysVisible.

Fixes http://b/issue?id=1978935