Add new config and API for QuickAccessWallet features.

Adds a new configuration attribute for use in
QuickAccessWalletService:
* useTargetActivityForQuickAccess - this is a boolean, false by default.
When true, the system will use the component specified by the
android:targetActivity attribute instead of the SysUi's WalletActivity.

Adds a new API method to QuickAccessWalletService: the method returns a
PendingIntent that can be used in place of the targetActivity specified
in the service's manifest entry. The method is not abstract; by default
it returns null so that existing services will not have to make any
changes to target android T.

To make use of this feature, define a new method in
QuickAccessWalletClient: useTargetActivityForQuickAccess() which
provides the configuration for use by QuickAccessWalletController.

Updates QuickAccessWalletController to define a new method: startQuickAccessUiIntent(),
which reads the configuration as well as whether the service is
providing any cards, and provides a centralized place to launch
the correct Quick Access intent.
The logic there is:
1. If a PendingIntent is provided from the service, use that.
2. If not, check for an active activity from the metadata in XML.
3. If that isn't available OR useTargetActivityForQuickAccess is false and the system is displaying cards, use WalletActivity provided by SystemUi.

Addes tests for QuickAccessWalletController. CTS Test for
QuickAccessWalletClient has new tests in a separate change in the same
topic. In the course of development, discovered that unit tests for
QuickAccessWalletController has been failing for as long as a year. Will
fix that and update in a follow-up.

Test: atest QuickAccessWalletControllerTest
Test: atest QuickAccessWalletClientTest
Bug: 215725263

Change-Id: Ifa3427d5e6f6b02e4afffa40453d1cb0f4f8ed67