Create api_domain module type and its bp2build converter

This module does not have any build actions in Soong yet. It will be
converted to a Bazel target using bp2build, and API export will be run
on the generated Bazel target

Test: go test ./bp2build
Test: TH
Change-Id: I76df32bd9f23b60e746b2700af07668a2ed74844
diff --git a/android/Android.bp b/android/Android.bp
index e0ad58f..29a88f2 100644
--- a/android/Android.bp
+++ b/android/Android.bp
@@ -30,6 +30,7 @@
     srcs: [
         "androidmk.go",
         "apex.go",
+        "api_domain.go",
         "api_levels.go",
         "arch.go",
         "arch_list.go",