Enable metalava sandbox in StubLibraries.bp and ApiDocs.bp.

Test: built entire topic with and without RBE_METALAVA.
Change-Id: Ia5767debc713a420b8d008943903238413d0816d

ApiDocs.bp

@@ -91,6 +91,7 @@ droidstubs {
     arg_files: [
         "core/res/AndroidManifest.xml",
     ],
+    sandbox: true,
     args: metalava_framework_docs_args,
     write_sdk_values: true,
 }

StubLibraries.bp

@@ -60,6 +60,7 @@ stubs_defaults {
     ],
     api_levels_annotations_enabled: false,
     filter_packages: packages_to_document,
+    sandbox: true,
 }
 
 stubs_defaults {
@@ -377,6 +378,7 @@ droidstubs {
         "core/java/android/os/RemoteException.java",
         "core/java/android/util/AndroidException.java",
     ],
+    sandbox: true,
     installable: false,
     sdk_version: "core_platform",
     annotations_enabled: true,