Add START_CROSS_PROFILE_ACTIVITIES to startActivity

This allows holders of START_CROSS_PROFILE_ACTIVITIES permission to start an activity of the caller package in the other profile.

Test: atest CrossProfileAppsHostSideTest (with new tests in change I661d4b7132291950c8bcb4690d90154a78751b1e)
Ignore-AOSP-First: seeking internal review on WIP change prior to merging in AOSP
Bug: 207117478
Change-Id: I5afa2e458b2eda4f53cfceabe3af950c0df63ad7