Add scripts/test_utils.sh to run tests without atest

This CL adds some useful bash functions that can be used to run tests
without atest. This is motivated by go/sysui-soong-gradle-comparison,
which showed that atest has a noticeable overhead compared to manually
building and running tests.

Usage:
  $ source build/envsetup.sh
  $ lunch <target>
  $ source ${ANDROID_BUILD_TOP}/frameworks/base/packages/SystemUI/scripts/test_utils.sh
  $ make_run_sysui_tests com.android.systemui.scene.domain.interactor.SceneInteractorTest

Inspired by go/sysui-cheatsheet#running-platformscenariotests-quickly.

Bug: 307607958
Test: Used the different functions to run tests
Flag: TEST_ONLY
Change-Id: Ie66966aa2d231b7a88dcc90a09e9e8017fbe1d2f