Do not auto-pip on launching translucent activity

Note we only prevent Activity from auto-pip in this case. Launching a
translucent Activity still sets ActivityTaskSupervisor#mUserLeaving to
be true and a non-auto-pip Activity will request to enter PiP when they
receive the onUserLeaveHint callback.

Bug: 245735998
Test: `adb shell am start -n <translucent-activity>` over YT
Test: atest PinnedStackTests
Change-Id: Iee4dc55592d3e9851174d18759917dd14f5c0071