Fix Keyboard overlap with navigation bar

FLAG_FULLSCREEN is really the wrong flag for determining whether
to subtract the window insets in the decore view and layout
it with a reduced size - FLAG_LAYOUT_IN_SCREEN suits these needs
much better.

Bug: 26014496
Bug: 26984057
Change-Id: I5c7a0fb7468d3981b91b23aa4c8b1e4841202131