Fix QR code scanner layout in "Pair devices over Wi-Fi" page.

The toolbar needs to be disabled to remove the empty space at the top
of the page. Also added the landscape layout xml.

Bug: 193602141
Test: atest SettingsUnitTests and manual

Change-Id: I30368835979b360a8f09e16f70adf57064784517
(cherry picked from commit fd009229e5)

AndroidManifest.xml

@@ -2188,6 +2188,8 @@
         <activity android:name=".development.AppPicker"
                   android:label="@string/select_application" />
 
+        <activity android:name=".development.AdbQrCodeActivity" />
+
         <activity android:name=".development.DSULoader"
                   android:label="Select DSU Package"
                   android:theme="@android:style/Theme.DeviceDefault.Light.Dialog" />