Use testapi to trigger gc in system and sysui

- Do this prior to gc'ing launcher to ensure that temporary binder
  refs on the system side a released

Bug: 186268407
Test: Presubmit

Change-Id: I7878e1042b07ded5491af6153cff9b0772c557db
diff --git a/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java b/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java
index e5b93b1..02ea82e 100644
--- a/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java
+++ b/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java
@@ -1349,6 +1349,8 @@
     }
 
     public int getTotalPssKb() {
+        // GC the system & sysui first before gc'ing launcher
+        logShellCommand("cmd statusbar run-gc");
         return getTestInfo(TestProtocol.REQUEST_TOTAL_PSS_KB).
                 getInt(TestProtocol.TEST_INFO_RESPONSE_FIELD);
     }