Send KEYCODE_HOME for home button instead of startActivity directly

Also updated calls to onBackEvent to match new signature of
including displayId.

Bug: 381339822
Flag: com.android.launcher3.home_button_uses_keycode_home
Test: manual, also OverviewCommandHelperTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:9ba5fcaffa95621af543be20851806f7dec88183)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:646dfdffb40a2ee31ea5d9fde44a320436b27ff5
Merged-In: I6e1272e1526e8b136376852f8ff50e3fa68bbede
Change-Id: I6e1272e1526e8b136376852f8ff50e3fa68bbede
9 files changed