Fix back gesture / keycode for the PlatLogoActivity

By overriding onKeyUp on the Activity itself, without
calling super, I broke legacy back handling. Fortunately,
there is now a better way to handle back!

(Also fix the theme to avoid wallpaper showing through
display cutout insets.)

Test: adb shell input keyevent --longpress KEYCODE_BACK
Test: swipe from edge
Fixes: 289648693
Fixes: 290989795
(cherry picked from commit 5bbab52e0062877e17579bec48031f06ded79963)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:eeacd7d3f11f204057da54a8229eab3b18a08a93)
Merged-In: I4fd4975421d204f06dbd8acda1a0d2a5a99f3465
Change-Id: I4fd4975421d204f06dbd8acda1a0d2a5a99f3465

core/res/AndroidManifest.xml

diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 2f9f6ae..4dbc54f 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -7752,8 +7752,9 @@
                 android:process=":ui">
         </activity>
         <activity android:name="com.android.internal.app.PlatLogoActivity"
-                android:theme="@style/Theme.Wallpaper.NoTitleBar.Fullscreen"
+                android:theme="@style/Theme.NoTitleBar.Fullscreen"
                 android:configChanges="orientation|screenSize|screenLayout|keyboardHidden"
+                android:enableOnBackInvokedCallback="true"
                 android:icon="@drawable/platlogo"
                 android:process=":ui">
         </activity>