ThemePicker: "Apply theme" initial implementation

Use the current API to apply the packages for a given theme.
Still pending is storing the applied overlay packages, and applying the
default theme.

Bug: 120559294

Change-Id: I7c15f8ab94b1dec8576141eaecd4f3e059249fb1
diff --git a/res/layout/fragment_theme_picker.xml b/res/layout/fragment_theme_picker.xml
index 0fd4044..ef40334 100644
--- a/res/layout/fragment_theme_picker.xml
+++ b/res/layout/fragment_theme_picker.xml
@@ -46,6 +46,7 @@
             android:layout_width="match_parent"
             android:layout_height="wrap_content">
             <Button
+                android:id="@+id/apply_button"
                 style="@style/ActionPrimaryButton"
                 android:layout_width="wrap_content"
                 android:layout_height="wrap_content"