Update the specification in the newly added constructors

Looks like different people use a different style for the new constructors, it will be good to unify them.

    * The text "Constructor for subclasses to call." should be used in the protected constructors in the abstract classes
    * In all other cases the text "Constructs an {@code ClassName}." should be used
    * A period (full stop) to the end of all javadoc comments, should be added if it is missing

I have started from https://bugs.openjdk.java.net/browse/JDK-8252721
See
https://bugs.openjdk.java.net/browse/JDK-8252908?focusedCommentId=14370006&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14370006

But since I already touched a bunch of classes, I decided to update some other fixes as well.

This will update the changes for:
https://bugs.openjdk.java.net/browse/JDK-8252721
https://bugs.openjdk.java.net/browse/JDK-8252195
https://bugs.openjdk.java.net/browse/JDK-8250858