Support CAST V2 authentication

bug: 12702350

Squashed commit of these CLs from the widevine cdm repo:

Cast V2 cdm support
https://widevine-internal-review.googlesource.com/#/c/9190/

Add CASTv2 Support to DrmPlugin
https://widevine-internal-review.googlesource.com/#/c/9228/

Test for CastV2 authentication APIs
https://widevine-internal-review.googlesource.com/9550

Change-Id: I6d66bc1bbd653db5542c68687b30b441dd20617f

libwvdrmengine/test/castv2/res/layout/main.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+  android:layout_width="fill_parent"
+  android:layout_height="fill_parent"
+  android:orientation="vertical">
+</LinearLayout>

libwvdrmengine/test/castv2/res/values/strings.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string name="app_name">CastSignAPI Test</string>
+</resources>