Replace art_cts_jvmti_test_library filegroup with java_library

This is to allow the art_cts_jvmti_test_library to be exported as part
of the ART module exports.

Bug: 142947124
Test: atest -p cts/hostsidetests/jvmti
Change-Id: I7ce0c78b8f40d928798764d74add8dbff4353af8
diff --git a/test/Android.bp b/test/Android.bp
index 6fc2fa4..c19bb73 100644
--- a/test/Android.bp
+++ b/test/Android.bp
@@ -604,7 +604,7 @@
     ],
 }
 
-filegroup {
+java_library {
     name: "art_cts_jvmti_test_library",
     visibility: [
         "//cts/hostsidetests/jvmti:__subpackages__",