Move robolectric tests from 3.6.2 to 4.8.2

Bug: 254010474
Test: m RunWallPaperPicker2RoboTests
Change-Id: Ib6af918b5de1115682627c8c287a07e6014b1462
diff --git a/robolectric_tests/Android.mk b/robolectric_tests/Android.mk
index 666c08d..e66a3c7 100644
--- a/robolectric_tests/Android.mk
+++ b/robolectric_tests/Android.mk
@@ -24,12 +24,13 @@
 LOCAL_SDK_VERSION := current
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 LOCAL_STATIC_JAVA_LIBRARIES := \
+    androidx.test.core \
     androidx.test.runner \
     androidx.test.rules \
     mockito-robolectric-prebuilt \
     truth-prebuilt
 LOCAL_JAVA_LIBRARIES := \
-    platform-robolectric-3.6.2-prebuilt
+    platform-robolectric-4.8.2-prebuilt
 
 LOCAL_JAVA_RESOURCE_DIRS := config
 
@@ -56,4 +57,4 @@
 
 LOCAL_ROBOTEST_TIMEOUT := 36000
 
-include prebuilts/misc/common/robolectric/3.6.2/run_robotests.mk
+include prebuilts/misc/common/robolectric/4.8.2/run_robotests.mk