CrossProfileApps#startActivity by intent starts in same task by default

This is based on developer feedback from Google Calendar. Tweak the API
to take in the calling activity.

Javadoc in ActivityTaskManagerInternal's new method is copied from the
existing method.

Bug: 149677845
Bug: 136249261
Test: atest com.android.cts.devicepolicy.CrossProfileAppsHostSideTest#testStartActivityIntent_sameTaskByDefault
Change-Id: I2f2d4d8fd82febf4916ba70a08de5e71c678a1f4