Migrate computeImeDisplayIdForTarget to ImeVisibilityStateComputer

To abtract the IME display computatation and this CL should not have any
behavior change.

Bug: 246309664
Test: atest CtsInputMethodTestCases InputMethodManagerServiceTests
Change-Id: I9e15358a1b101a526828115245a85964f06da4bd
2 files changed