Move mImeWindowVis and mBackDisposition to binding controller

Make mImeWindowVis and mBackDisposition per user by moving it to
binding controller.

This code change is an internal refactoring and should not cause
any noticeable issues on surfaces with non-concurrent multi-user IME
enabled.

Bug: 325515685
Test: atest FrameworksInputMethodSystemServerTests
Test: atest CtsInputMethodTestCases
Test: atest FrameworksServicesTests
Test: atest --host FrameworksInputMethodSystemServerTestsRavenwood
Flag: EXEMPT refactor
Change-Id: I11a7905cd4fd08a21e5d29da0ee9ded17f081abd