Load enterprise thumbnail drawable only if needed

It can save ~30% to construct an ActivityRecord.
Especially since shell transition is enabled, it will be handled
in DefaultTransitionHandler#mEnterpriseThumbnailDrawable, then
the drawable in ActivityRecord is never used.

Bug: 297502610
Test: Launch app of profile user by
      CrossProfileApps#startMainActivity
Change-Id: I0ecc1732c902ef53a7f16b4e90bcdfc75a6c1c73