Fix flicker when hiding the IME in horizontal split screen

In a hide IME animation in horizontal split screen, the WindowContainer#mExcludeInsetsTypes were reset too early (before the IME requested visibility was dispatched). Thus, IME insets were dispatched as visible, but immediately afterwards (when IME visibility was set) as hidden.
By calling dispatchEndPositioning only after the IME visibility was sent, this will be fxed.

Fix: 381134667
Test: Hide IME in vertical split screen, verify that there is no flicker
Flag: android.view.inputmethod.refactor_insets_controller
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:9a7d8912e7d3f12550675356c00b8330b039aec6)
Merged-In: Ia2f427dc8902273562c1d848d2805e1ee66c2395
Change-Id: Ia2f427dc8902273562c1d848d2805e1ee66c2395