RFR: 8277459: Add jwebserver tool

[Julia Boes]

On Mon, 22 Nov 2021 09:43:19 GMT, Julia Boes <jboes at openjdk.org> wrote:

> This change introduces jwebserver, a dedicated JDK tool for the Simple Web Server. 
> 
> A description is provided in a follow-up comment.

This change adds a dedicated command-line tool for the Simple Web Server, to improve convenience and approachability. The new tool `jwebserver` calls the main entry point of the jdk.httpserver module, thus hiding this implementation detail which is not hidden with `java -m jdk.httpserver`. The command-line options are identical, the only addition is support for `-version` / `--version`. 

A man page for `jwebserver` is added and the module and package level documentation is updated to reflect the new tool.

A new internal class JWebServer is added to be able to distinguish whether the server was launched via `jwebserver` or `java -m jdk.httpserver`.

The new tests are copies of the existing command-line tests.

CSR: https://bugs.openjdk.java.net/browse/JDK-8277460

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PR: https://git.openjdk.java.net/jdk/pull/6497