Build updatable-bcp-packages.txt from prebuilts in sdk snapshot

Previously, the java_import and java_sdk_library_import modules did not
make their permitted_packages available to the rule that generates the
updatable-bcp-packages.txt file. This change corrects that.

Bug: 193095050
Test: m nothing
      - Added unit tests, which all failed and then fixed the tests.
Merged-In: If0706e4551a331b48d383123088e63924dded48b
Change-Id: If0706e4551a331b48d383123088e63924dded48b
(cherry picked from commit 630b11e9d4d63e5fabaa20adf5d1b1c81ede6681)
diff --git a/java/sdk_library.go b/java/sdk_library.go
index c0e5662..8c66438 100644
--- a/java/sdk_library.go
+++ b/java/sdk_library.go
@@ -1991,6 +1991,12 @@
 	return module
 }
 
+var _ PermittedPackagesForUpdatableBootJars = (*SdkLibraryImport)(nil)
+
+func (module *SdkLibraryImport) PermittedPackagesForUpdatableBootJars() []string {
+	return module.properties.Permitted_packages
+}
+
 func (module *SdkLibraryImport) Prebuilt() *android.Prebuilt {
 	return &module.prebuilt
 }