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)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4758973488ef3f85483a52f08d0bfc87954ad2e7)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5bac97af31ef8ae48e5c49effcf7231d02a234d0)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:979a35df7aa7e9cb153409abc3b96861b2581ca1)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b91ab66683ae04842c8c8eac6ec61a407416826c)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c652ca9ea210336af22cf8191f723ba1a0f352b0)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:5625c5b8a621b7daf5945764905402ff121b8429)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:2f9f1570f46547ba07a8b28bdaa2f1b482441912
Merged-In: I6e1272e1526e8b136376852f8ff50e3fa68bbede
Change-Id: I6e1272e1526e8b136376852f8ff50e3fa68bbede