Add testAPIs in ContentCaptureManager

Added the following static testAPIs to replace
the usage of adb commands in cts/gts tests:
* resetTemporaryService
* setTemporaryService
* setDefaultServiceEnabled
These APIs are static because by default ContentCaptureManager
isn't available until it's enabled using these APIs.

Test: Confirmed that the APIs are accessible in CTS tests.
Bug: 180328483
Change-Id: I0a94d90b509e1d2f695556955d85d27acab19ae9