DisplayImeController: reapply visibility when leash changes

Fixes an issue where the DisplayImeController did not re-apply the visibility
if it receives a new leash.

This lead to focusable IME dialogs not being visible sometimes upon relaunching
the IME target activity, such as during rotation.

Fixes: 162875596
Bug: 160672060
Test: Enable Braille keyboard, open Settings, click on search box, switch to Braille keyboard, on the confirmation dialog rotate the screen; verify the dialog does not disappear.
Change-Id: Ia40a682ca8a9ba669454892e2b453f736c55929c
Merged-In: Ia40a682ca8a9ba669454892e2b453f736c55929c