Add APIs to allow app to share identity with launched activity

This commit adds APIs to allow a launching app to share its identity
with a launched activity without needing to call
startActivityForResult and to allow the launched activity to obtain
the uid and package name of the launching app.

Bug: 259743961
Test: atest CtsAndroidAppTestCases:android.app.cts.ShareIdentityTest
Change-Id: Ib10496c031ddf12d7c362dcaca04ef1560ef11cc