Change bp2build converter of module "package".

1) Use attribute name "default_package_metadata" instead of
   "default_applicable_licenses" in packages to better describe its use.
2) Add a filegroup "default_metadata_file" in packages to search for
   METADATA file in each package.
3) Include "default_metadata_file" in each package's
   "default_package_metadata" attribute.

Bug: 275472038
Test: CIs
Change-Id: I645c013c39e3190fd96c4a549d39a331aced16bd
diff --git a/android/filegroup.go b/android/filegroup.go
index 0ca5dc5..f30ee51 100644
--- a/android/filegroup.go
+++ b/android/filegroup.go
@@ -75,7 +75,8 @@
 
 // https://docs.bazel.build/versions/master/be/general.html#filegroup
 type bazelFilegroupAttributes struct {
-	Srcs bazel.LabelListAttribute
+	Srcs                bazel.LabelListAttribute
+	Applicable_licenses bazel.LabelListAttribute
 }
 
 type bazelAidlLibraryAttributes struct {