Add SourceVersion.RELEASE_10

Summary

Add the constant RELEASE_10 to the SourceVersion enum.

Problem

With a new release, a matching new SourceVersion constant is needed.

Solution

Add the new constant.

Specification

-     RELEASE_9;
+     RELEASE_9,
+
+    /**
+     * The version recognized by the Java Platform, Standard Edition
+     * 10.
+     *
+     * @since 10
+     */
+     RELEASE_10;