Droiddoc Support in Soong

Support Droiddoc to Soong based on core/droiddoc.mk. The non-std doclet
based droiddoc compilation output is a "real" stubs.jar instead of a
directory of java files and a timestamp file.

The std doclet based javadoc compilation output is a "empty" stubs.jar
instead of a timestamp file.

The stubs.jar will be exported to
out/target/common/obj/JAVA_LIBRARIES/$(LOCAL_MODULE)_intermediates/classes.jar
and out/target/common/docs/$(LOCAL_MODULE)-stubs.jar

A $(LOCAL_MODULE).zip file will be generated also, and is exported to
out/target/common/docs/$(LOCAL_MODULE)-docs.zip if property: installable is not set
to false.

Bug: b/70351683
Test: unittest + convert libcore docs Android.mk to Soong manually.

Change-Id: I1cffddd138a5d9d445f86a3d4a3fd4de88a2bc0f
(cherry picked from commit 78188ec622cb1ee24171455867fc58ffab91562e)

java/java.go

@@ -538,8 +538,8 @@ func (j *Module) aidlFlags(ctx android.ModuleContext, aidlPreprocess android.Opt
 }
 
 type deps struct {
-	classpath          android.Paths
-	bootClasspath      android.Paths
+	classpath          classpath
+	bootClasspath      classpath
 	staticJars         android.Paths
 	staticHeaderJars   android.Paths
 	staticJarResources android.Paths
@@ -688,8 +688,8 @@ func (j *Module) collectBuilderFlags(ctx android.ModuleContext, deps deps) javaB
 	}
 
 	// classpath
-	flags.bootClasspath.AddPaths(deps.bootClasspath)
-	flags.classpath.AddPaths(deps.classpath)
+	flags.bootClasspath = append(flags.bootClasspath, deps.bootClasspath...)
+	flags.classpath = append(flags.classpath, deps.classpath...)
 
 	if len(flags.bootClasspath) == 0 && ctx.Host() && !ctx.Config().TargetOpenJDK9() &&
 		!Bool(j.properties.No_standard_libs) &&
@@ -836,7 +836,7 @@ func (j *Module) compile(ctx android.ModuleContext, extraSrcJars ...android.Path
 		}
 
 		if enable_sharding {
-			flags.classpath.AddPaths([]android.Path{j.headerJarFile})
+			flags.classpath = append(flags.classpath, j.headerJarFile)
 			shardSize := int(*(j.properties.Javac_shard_size))
 			var shardSrcs []android.Paths
 			if len(uniqueSrcFiles) > 0 {