Add package filter for system_server stubs

Should prevent accidental addition of APIs outside com.android,
which is where we want these APIs to be.

Also fix a bug in the permission filegroup where it wasn't
specifying the subpath of its code.

Bug: 149293194
Test: m update-api
Change-Id: I144ce6dbfe524106fc7de87318f66390c31b45af

apex/Android.bp

@@ -137,6 +137,7 @@ stubs_defaults {
     name: "service-module-stubs-srcs-defaults",
     args: mainline_service_stubs_args,
     installable: false,
+    filter_packages: ["com.android."],
     check_api: {
         current: {
             api_file: "api/current.txt",

apex/permission/service/Android.bp

@@ -17,6 +17,7 @@ filegroup {
     srcs: [
         "java/**/*.java",
     ],
+    path: "java",
 }
 
 java_library {

services/Android.bp

@@ -126,6 +126,7 @@ droidstubs {
         " --hide DeprecationMismatch" +
         " --hide HiddenTypedefConstant",
     visibility: ["//visibility:private"],
+    filter_packages: ["com.android."],
     check_api: {
         current: {
             api_file: "api/current.txt",