Summary
-------

Update informative description of `SourceVersion.RELEASE_14` to mention switch expressions.

Problem
-------

The summary of the new features in the release is out of date.

Solution
--------

Update the feature list of the release to include switch expressions.

Specification
-------------

         /**
          * The version recognized by the Java Platform, Standard Edition
          * 14.
          *
    +     * Additions in this release include switch expressions.
    +     *
          * @since 14
          */
          RELEASE_14;