Use handcrafted build targets in bp2build

If both bp2build_available and label are specified, label will be
preferred.

Initially, we copy the entire BUILD.bazel file. Eventually we may move
this to use bazel query for a more accurate result.

Test: go test *
Test: build/bazel/scripts/milestone-2/demo.sh full
Test: GENERATE_BAZEL_FILES=true m nothing
      edit bionic/libc/tools/BUILD.bazel
      GENERATE_BAZEL_FILES=true m nothing and verify changes picked up
Bug: 180516554
Change-Id: I43025583300e6b10d2c18032cd4a76237b578d59

cmd/soong_build/main.go

@@ -198,7 +198,6 @@ func runBp2Build(srcDir string, configuration android.Config) {
 	if err != nil {
 		panic(err)
 	}
-	extraNinjaDepsString := strings.Join(extraNinjaDeps, " \\\n ")
 
 	// Run the loading and analysis pipeline to prepare the graph of regular
 	// Modules parsed from Android.bp files, and the BazelTargetModules mapped
@@ -215,6 +214,9 @@ func runBp2Build(srcDir string, configuration android.Config) {
 	// 1:1 mapping for each module.
 	metrics.Print()
 
+	extraNinjaDeps = append(extraNinjaDeps, codegenContext.AdditionalNinjaDeps()...)
+	extraNinjaDepsString := strings.Join(extraNinjaDeps, " \\\n ")
+
 	// Workarounds to support running bp2build in a clean AOSP checkout with no
 	// prior builds, and exiting early as soon as the BUILD files get generated,
 	// therefore not creating build.ninja files that soong_ui and callers of