Fix starting the activity with incorrect pid/uid

Starts the activity in the same thread vs. in the frame callback.

Bug: 406763872
Test: am start-in-vsync
Flag: EXEMPT bugfix

(cherry picked from commit fca9c788)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:c96de2de142edb854d39f5197c2f0fe6618aa482)
Merged-In: Ifb5e130a1e73e076233b6d78e2ab7bc118dce35b
Change-Id: Ifb5e130a1e73e076233b6d78e2ab7bc118dce35b