Add launcher extendible theme integration (2/3)

Flag: com.android.systemui.shared.extendible_theme_manager
Bug: 397782741
Test: manually verified
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c5612b3ff6fbf5cda8d8d1bffbec084a165e6c5b)
Merged-In: I36db3f88e9dd7ad8385d35c85d817bbd73beb9dd
Change-Id: I36db3f88e9dd7ad8385d35c85d817bbd73beb9dd