Test 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.

Note that although many of the test calls now pass in a null parameter,
this would be very unusual in reality. Most apps will be calling this
from an activity, so will just pass that activity in. Passing in null
here is just a side effect of a) running this from a CTS test app and b)
not caring about starting within the same task for the other tests.

Bug: 149677845
Bug: 136249261
Test: atest com.android.cts.devicepolicy.CrossProfileAppsHostSideTest#testStartActivityIntent_sameTaskByDefault
Change-Id: I60644b0c3a1ba3839ef41541b9a769cd48a87121