bp2build: framework for generating BazelTargetModules.

This CL creates the framework necessary for generating
BazelTargetModules from regular Soong Android modules.
BazelTargetModules are code-generated into Bazel targets in BUILD files.

See the follow-up CL for examples of creating filegroup/genrule
BazelTargetModules.

Test: GENERATE_BAZEL_FILES=true m nothing # creates out/soong/bp2build
with no BUILD files, because there are no BazelTargetModules in the
module graph.

Change-Id: I33a96365bd439043b13af6db9e439592e9983188
diff --git a/bp2build/Android.bp b/bp2build/Android.bp
index 49587f4..8007574 100644
--- a/bp2build/Android.bp
+++ b/bp2build/Android.bp
@@ -10,6 +10,7 @@
     ],
     deps: [
         "soong-android",
+        "soong-bazel",
     ],
     testSrcs: [
         "build_conversion_test.go",