Add package.html files to services metalava stubs

Metalava is reading the package.html files without dependencies,
and sandboxing it without providing package.html causes failures.

Bug: 153703940
Test: m services-stubs.sources services-non-updatable-stubs.sources
Change-Id: I4a34252beb17d8a99db1d630018dfe075ace79ba

services/Android.bp

@@ -9,7 +9,10 @@ package {
 
 filegroup {
     name: "services-main-sources",
-    srcs: ["java/**/*.java"],
+    srcs: [
+        "java/**/*.java",
+        "java/**/package.html",
+    ],
     path: "java",
     visibility: ["//visibility:private"],
 }
@@ -19,6 +22,7 @@ filegroup {
     srcs: [
         ":services.core-sources",
         ":services.core-sources-am-wm",
+        "core/java/com/android/server/am/package.html",
         ":services.accessibility-sources",
         ":services.appprediction-sources",
         ":services.appwidget-sources",