MultiUserPerfTest test switch to pre-existing user

Creates two new MultiUserPerfTests, timing how long it takes to switch
to a pre-existing user, one for when the user is already-started, and
the other for when it is stopped.

Bug: 126745587
Test: make MultiUserPerfTests && adb install -r ${ANDROID_PRODUCT_OUT}/data/app/MultiUserPerfTests/MultiUserPerfTests.apk && adb shell am instrument -e class android.multiuser.UserLifecycleTests -w com.android.perftests.multiuser/androidx.test.runner.AndroidJUnitRunner
Change-Id: I734f4971ad992e906a0090f4ef328255ab2a0349