Add outputfiles tags for droidstubs api txts

These can then easily be used in genrules to merge txt files.

Bug: 169034951
Test: m combined-dex-api
Change-Id: Id49739c90a2ab52a72094b76696a4e5211c8d742

java/droiddoc.go

@@ -1064,6 +1064,10 @@ func (d *Droidstubs) OutputFiles(tag string) (android.Paths, error) {
 		return android.Paths{d.stubsSrcJar}, nil
 	case ".docs.zip":
 		return android.Paths{d.docZip}, nil
+	case ".api.txt":
+		return android.Paths{d.apiFilePath}, nil
+	case ".removed-api.txt":
+		return android.Paths{d.removedApiFile}, nil
 	case ".annotations.zip":
 		return android.Paths{d.annotationsZip}, nil
 	case ".api_versions.xml":