Prepare to be able to put framework-res in srcs

This change introduces two changes required to put
framework-res explicitly in srcs property, without relying on the build
system to specially add framework-res as a dependency to
framework-minus-apex, etc.

1) R.java and Manifest.java generated from aapt were packaged to the file
R.jar directly under the gen directory. With this change, the file
becomes android/R.srcjar under the gen directory.

2) android_app module now overrides OutputFileProducer interface so that
it can recognize "{.aapt.srcjar}" tag to reference the generated srcjar file.

Being able to put framework-res in srcs allows us to pass all the source
files (both in the source tree and the ones generates) via a filegroup.
Previously, the source files could only be passed via the java_library
module type. This caused a circular dependency problem when the java
library was used as an input (src_libs) of the droiddoc module. Using
filegroup eliminates the circular dependency.

Bug: 70046217
Test: m

Merged-In: I9ab6116bcc6fa3da60933d427575463b05ae69b4
(cherry picked from commit 94f37f33ed)
Change-Id: I9ab6116bcc6fa3da60933d427575463b05ae69b4

java/app.go

@@ -539,6 +539,15 @@ func (a *AndroidApp) getCertString(ctx android.BaseModuleContext) string {
 	return String(a.overridableAppProperties.Certificate)
 }
 
+// For OutputFileProducer interface
+func (a *AndroidApp) OutputFiles(tag string) (android.Paths, error) {
+	switch tag {
+	case ".aapt.srcjar":
+		return []android.Path{a.aaptSrcJar}, nil
+	}
+	return a.Library.OutputFiles(tag)
+}
+
 // android_app compiles sources and Android resources into an Android application package `.apk` file.
 func AndroidAppFactory() android.Module {
 	module := &AndroidApp{}