Cherrypick aosp/1318079 and aosp/1324841

Allow apex module to have android_app_set as its constituent.
Fix android_app_set documentation

Fixes: 157166068
Test: treehugger & manual
Change-Id: I9f91f1b761286f489d175eb0772f78f702e8a2d6
Merged-In: I9f91f1b761286f489d175eb0772f78f702e8a2d6
Merged-In: Id9b296d9301902deb463b299413491bc66d58944

apex/apex.go

@@ -1150,6 +1150,7 @@ const (
 	javaSharedLib
 	nativeTest
 	app
+	appSet
 )
 
 func (class apexFileClass) NameInMake() string {
@@ -1164,7 +1165,7 @@ func (class apexFileClass) NameInMake() string {
 		return "JAVA_LIBRARIES"
 	case nativeTest:
 		return "NATIVE_TESTS"
-	case app:
+	case app, appSet:
 		// b/142537672 Why isn't this APP? We want to have full control over
 		// the paths and file names of the apk file under the flattend APEX.
 		// If this is set to APP, then the paths and file names are modified
@@ -1981,6 +1982,15 @@ func (a *apexBundle) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 					filesInfo = append(filesInfo, apexFileForAndroidApp(ctx, ap))
 				} else if ap, ok := child.(*java.AndroidTestHelperApp); ok {
 					filesInfo = append(filesInfo, apexFileForAndroidApp(ctx, ap))
+				} else if ap, ok := child.(*java.AndroidAppSet); ok {
+					appDir := "app"
+					if ap.Privileged() {
+						appDir = "priv-app"
+					}
+					af := newApexFile(ctx, ap.OutputFile(), ap.Name(),
+						filepath.Join(appDir, ap.BaseModuleName()), appSet, ap)
+					af.certificate = java.PresignedCertificate
+					filesInfo = append(filesInfo, af)
 				} else {
 					ctx.PropertyErrorf("apps", "%q is not an android_app module", depName)
 				}