Update IMM delegate if view root is moved to a different display

Although it makes sense to not get IMM delegate every time, the
instance may need to be refreshed if the associated display is
changed because InputMethodManager returns different instance for
different display.

Fix: 148189172
Test: atest MultiDisplayClientTests# \
            testDisplayIdUpdateWhenImeMove_NoRelaunchActivity

Change-Id: Id4c85be1c0eab51f167ba00fc355386f852c424d