Summary
-------
More clearly specify the value of the java.{vm.}?specification.version system properties.

Problem
-------
It hasn't been clear in the past how the java.{vm.}?specification.version property values relate to the "java.version" system property, or how the values might change in a Maintenance Release.

As of JEP 322 "Time-Based Release Versioning", we have a well-defined progression of FEATURE version numbers, and the "java.specification.version" and "java.vm.specification.version" system properties get their value from the VERSION_FEATURE make variable.

We can clarify what values to expect from the java.{vm.}?specification.version properties.

Solution
--------
In System.getProperties(), indicate that the value of the "java.specification.version" and "java.vm.specification.version" system properties come from the $FEATURE element of Runtime.Version.

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

        java.lang.System.getProperties()
        --------------------------------
    *** 605,616 ****
           * <tr><th scope="row">{@code java.vm.specification.version}</th>
    !      *     <td>Java Virtual Machine specification version which may be
    !      *     interpreted as a {@link Runtime.Version}</td></tr>
           * <tr><th scope="row">{@code java.vm.specification.vendor}</th>
    --- 605,617 ----
           * <tr><th scope="row">{@code java.vm.specification.version}</th>
    !      *     <td>Java Virtual Machine specification version, whose value is the
    !      *     {@linkplain Runtime.Version#feature feature} element of the
    !      *     {@linkplain Runtime#version() runtime version}</td></tr>
           * <tr><th scope="row">{@code java.vm.specification.vendor}</th>
    *** 619,630 ****
           * <tr><th scope="row">{@code java.specification.version}</th>
    !      *     <td>Java Runtime Environment specification version which may be
    !      *     interpreted as a {@link Runtime.Version}</td></tr>
           * <tr><th scope="row">{@code java.specification.vendor}</th>
    --- 620,632 ----
           * <tr><th scope="row">{@code java.specification.version}</th>
    !      *     <td>Java Runtime Environment specification version, whose value is
    !      *     the {@linkplain Runtime.Version#feature feature} element of the
    !      *     {@linkplain Runtime#version() runtime version}</td></tr>
           * <tr><th scope="row">{@code java.specification.vendor}</th>