Add a Tag field to dist to dist a tagged output

Make java_library support this mode of output, to allow
callers to dist the classes.jar file rather than the dexed
jar file.

Bug: 152618077
Test: followup CL
Change-Id: I5ba6949833a0fbb95376142aec5096ff5f084c00

java/androidmk.go

@@ -72,6 +72,7 @@ func (library *Library) AndroidMkEntries() []android.AndroidMkEntries {
 	if !hideFromMake {
 		mainEntries = android.AndroidMkEntries{
 			Class:      "JAVA_LIBRARIES",
+			DistFile:   android.OptionalPathForPath(library.distFile),
 			OutputFile: android.OptionalPathForPath(library.outputFile),
 			Include:    "$(BUILD_SYSTEM)/soong_java_prebuilt.mk",
 			ExtraEntries: []android.AndroidMkExtraEntriesFunc{