RFR: 8350007: Add usage message to the javadoc executable

[Nizar Benalla]

On Thu, 13 Feb 2025 16:41:54 GMT, Nizar Benalla <nbenalla at openjdk.org> wrote:

> This patch adds a new message when you run the `javadoc` executable with any arguments.
> Currently, unlike most other tools, running `javadoc` without any arguments does not show you how to use the tool or point you to use the `--help` option, this can be improved.
> 
> Before change:
> 
> W $ ./javadoc
> error: No modules, packages or classes specified.
> 1 error
> 
> 
> After change:
> 
> W $ ./javadoc
> Usage:
>     javadoc [options] [packagenames] [sourcefiles] [@files]
> For additional help on usage:           javadoc --help

I had only run the `langtools_javadoc` tests and missed this `javac` failure.

There is a change to a compiler test.

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PR Comment: https://git.openjdk.org/jdk/pull/23618#issuecomment-2659124543
PR Comment: https://git.openjdk.org/jdk/pull/23618#issuecomment-2659127237