[bp2build] android_test bp2build.

android_test is just an android_app, but the test bits are handled
purely in Starlark (tradefed_test_impl).

This enables building HelloWorldTests (android_test) with Bazel.

Bug: 297030120
Bug: 297029612
Test: WIP
Change-Id: I6d287c94b31698ea247da48e4cd6b5a75bc71e11
diff --git a/java/aar.go b/java/aar.go
index 0216196..73f9ff1 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -1340,7 +1340,10 @@
 	if !commonAttrs.Srcs.IsEmpty() {
 		deps.Append(depLabels.StaticDeps) // we should only append these if there are sources to use them
 	} else if !depLabels.Deps.IsEmpty() {
-		ctx.ModuleErrorf("Module has direct dependencies but no sources. Bazel will not allow this.")
+		ctx.MarkBp2buildUnconvertible(
+			bp2build_metrics_proto.UnconvertedReasonType_UNSUPPORTED,
+			"Module has direct dependencies but no sources. Bazel will not allow this.")
+		return
 	}
 	name := a.Name()
 	props := AndroidLibraryBazelTargetModuleProperties()