Move the descriptorset output to the ProtoSourcesProvider and expose it to skylark.

This does mean that the type name 'ProtoSourcesProvider' is a little inaccurate, since descriptorSet() is an output.  Alternatively we could expose the DescriptorSetProvider to skylark.


RELNOTES: expose proto_library descriptor set to skylark via <dep>.proto.descriptor_set

--
PiperOrigin-RevId: 142680666
MOS_MIGRATED_REVID=142680666

src/test/java/com/google/devtools/build/lib/BUILD

diff --git a/src/test/java/com/google/devtools/build/lib/BUILD b/src/test/java/com/google/devtools/build/lib/BUILD
index 6761357..40c40b9 100644
--- a/src/test/java/com/google/devtools/build/lib/BUILD
+++ b/src/test/java/com/google/devtools/build/lib/BUILD
@@ -1220,6 +1220,7 @@
         ":actions_testutil",
         ":analysis_testutil",
         "//src/main/java/com/google/devtools/build/lib:build-base",
+        "//src/main/java/com/google/devtools/build/lib:proto-rules",
         "//src/main/java/com/google/devtools/build/lib/actions",
         "//third_party:junit4",
         "//third_party:truth",