Integrate lost clhsdb documenation

In the open repo we have the src/jdk.hotspot.agent/doc directory, which has (often outdated) SA documentation. This documentation does not get published, and for the most part this has been replaced by the man page for jhsdb, which is maintained in the closed repo. However, there are parts of this open documentation that are not incorporated in any fashion in the jhsdb man page.

The main part that is not covered by the jhsdb man page is the contents of clhsdb.html. Although the jhsdb man page does document the clhsdb sub-command, all it says about it is "Starts the interactive command-line debugger." The clhsdb.html page lists all of the clhsdb commands, with a brief description of each. This is more than the help output you get with the clhsdb "help" command, which only lists the commands (and options syntax), but does not describe them in any way. Although the help text in clhsdb.html is brief, it is better than nothing.

Another thing we get from src/jdk.hotspot.agent/doc is a brief overview of SA in the index.html file. Although outdated and too brief, this is also something we don't have in the jhsdb man page.

It would be nice if we could publish the src/jdk.hotspot.agent/doc documentation, tie it in with the jhsdb man page, and also improve it. The main thing that could us improving is the contents of clhsdb.html. The description of each clhsdb command is too terse and could use examples in some instances.

Also see JDK-8279121, which talks about shortcoming of the clhsdb documentation, and suggestions for improving it. We may just choose to improve the clhsdb help output rather than having online docs.