Introduced the DefaultAccountAndState class in the ContactsContract

class.

Bug: 359957527
Test: added new CTS test
Flag:android.provider.new_default_account_api_enabled
Bypass: test failure
[Test:Module] MediaProviderTests in v2/android-virtual-infra/test_mapping/presubmit-avd on aosp_cf_x86_64_only_phone-trunk_staging-userdebug on git_main (which is unrelated to this change)

This will be Step 1 of 3 in the new Default account getter/setter
API:

Step 1 - Define DefaultAccountAndState class in the ContactsContract.
Step 2 - Implement the getter/setter handler in ContactsProvider call
         method.
Step 3 - Define the getter/setter API in the ContactsContract, which
         envokes the ContentResolver.call utlimaitely handled by
	 ContactsProvider's getter/setter call implemented in Step 2.

	modified:   core/java/android/provider/ContactsContract.java
	modified:   core/java/android/provider/flags.aconfig

Change-Id: Ic79750d713b2a5826c4214719f8079b4986f90b4