Stop hiding the IME window when turning screen off

In [1] we introduced the IME Screenshot, a layer to be shown when
navigating away from an app that has the IME visible, to avoid flickers.
Later in [2] we started explicilty hiding the IME window when the screen
is turning off, as the IME Screenshot would be visible on top of it
anyway. In [3], we started allowing the IME screenshot for activities of
type home or recent (previously omitted as an optimization), to attempt
to prevent a flicker.

However, hiding the IME explicitly so early still causes flickers.
Moreover, when we capture the AppSnapshot before turning the screen off,
the IME might be previously visible, but marked hidden at the time of
the snapshot capture, which disallows skipping the next IME show
animation when unlocking the screen.

This removes the explicit hiding of the IME window, as well as the extra
case of allowing the IME Screenshot on home or recents activites in the
screen turning off scenario.

  [1]: I6bef36c779a28777408576f57e5d1c67d5d48e3f
  [2]: I2e1e4bc106fc14aa65825ee82dc09390422951c5
  [3]: I1132a78ba1154e777a9751ac70659cd6377fcb39

Flag: EXEMPT bugfix
Test: atest com.android.server.wm.flicker.ime.ShowImeOnUnlockScreenTest
Bug: 426546412
Bug: 426548274
Bug: 384853532
Change-Id: Ia68ed50247034553760b5b9ec794122ee4930777