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)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:063dd3bcdd0dcbff5be4f53a6f39c4070f76706b)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:c16b86ca2e8fbc0b830870b65e7622ba9b8c20cb
Merged-In: I6e1272e1526e8b136376852f8ff50e3fa68bbede
Change-Id: I6e1272e1526e8b136376852f8ff50e3fa68bbede