Reapply "Move widget picker tests to Robolectric"

This reverts commit 97ee134a.

Reason for revert: Fixed an issue with UI_HELPER_EXECUTOR that caused the flakiness

Test: atest NexusLauncherRoboTests
Test: SysUI studio
Flag: None Test migration
Fix: 325088642
Fix: 325088805
Fix: 325089116
Fix: 325088960

Change-Id: I2f50c30d2c861e3bba8a8fa3ec547ca2ade6153a