Implement bp2build for the `package` module

* We are interested mostly in the conversion the `default_applicable_licenses`
  attribute, as `default_visibility` cannot be handled until every module's
  `visibility` is handled.
* Several referenced license modules had to be manually enabled for
  conversion, and likewise a few trivial Android.bp containing only
  package and license modules.
* As Bazel allows only a single `package` rule, the package rules in a
  manually converted BUILD.bazel files were removed (in
  external/protobuf and prebuilts/clang/host/linux-x86 trees).
* The converted package rule is emitted before the `load` statements per
  Bazel documentation.

Bug: 190817312
Test: treehugger
Change-Id: If8bf6fee1580177de3bb402923615bcd48923ed2
diff --git a/tests/lib.sh b/tests/lib.sh
index 7248ade..4b4d908 100644
--- a/tests/lib.sh
+++ b/tests/lib.sh
@@ -123,6 +123,7 @@
   symlink_directory prebuilts/jdk
   symlink_directory external/bazel-skylib
   symlink_directory external/bazelbuild-rules_android
+  symlink_directory external/bazelbuild-rules_license
   symlink_directory external/bazelbuild-kotlin-rules
 
   symlink_file WORKSPACE