RFR: 8303410: Remove ContentSigner APIs and jarsigner -altsigner and -altsignerpath options [v4]

[Eirik Bjorsnos]

On Thu, 9 Mar 2023 18:50:42 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> The `-altsigner` and `-altsignerpath` options in JarSigner with the underlying `ContentSigner` mechanism were deprected in Java 9, for removal in Java 15. See [JDK-8076535](https://bugs.openjdk.org/browse/JDK-8076535), [JDK-8242260](https://bugs.openjdk.org/browse/JDK-8242260).
>> 
>> This PR suggests it's time to remove this code:
>> 
>> - The package `com/sun/jarsigner` is removed. This contained the `ContentSigner` and `ContentSignerParameters` along with a `package-info.java` file.
>> - `JarSigner.java` is updated to remove processing of the `-altsigner` and `-altsignerpath` options and the loading and processing of the custom `ContentSigner`.
>> - Similarly `c.s.s.t.jarsigner.Main` is updated to remove processing and mentioning of `-altsigner` and `-altsignerpath` options.
>> - Mentions of the options in Resource files in the same directory is removed
>> - The `jarsigner.1` man page is updated to remove the section on the deprecated options
>> - The `Spec` and `Options` tests are update to remove usage of the `-altsigner` and `-altsignerpath` options.
>
> Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unused resource names 'This.option.is.forremoval' and 'using.an.alternative.signing.mechanism'

Thanks for reviewing Weijun!

I'll let this simmer for a bit before integrating just in case someone else would want to have a look.

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PR: https://git.openjdk.org/jdk/pull/12791