ci: manage XMLResolver.org XML Resolver version

[AirQuick]

While XML resolver in general plays a critical role, it can be buggy.
Now, Saxon, XML Calabash and Oxygen come bundled with different versions of XMLResolver.org XML Resolver. So, when a problem happens, it's getting hard to spot where the problem is.

This pull request deletes the bundled versions and install a specific version before running the tests.
With this change, we will be able to

• Test with the latest version as soon as it's released.
• Skip buggy versions.

[galtm]

I think this change is well motivated and well executed, including helpful comments. It might even enable XSpec to detect and report a relevant XML Resolver bug sooner.

My only concern about overriding the bundling is that it could mask problems that end users experience when using the bundled version of the XMLResolver.org XML Resolver application. I think we can mitigate that risk through our own awareness, though. If a user reports a problem that isn't reproducible via the XSpec test suite, we should check whether the XML Resolver version is a difference between the test suite's environment and the user's environment.

One question: Are you thinking that the XSpec testing should routinely update the XMLResolver.org XML Resolver version, even if XML Calabash and Saxon have not adopted the new version yet and updating is not needed as a bug workaround? You wrote "able to Test with the latest version as soon as it's released" and my question is whether you see that as more of a theoretical capability or an operating standard.

[AirQuick]

Are you thinking that the XSpec testing should routinely update the XMLResolver.org XML Resolver version, even if XML Calabash and Saxon have not adopted the new version yet and updating is not needed as a bug workaround?

Yes, I think we should always keep the XMLResolver.org XML Resolver base version updated. That would prevent a buggy version from being shipped with Saxon.

[galtm]

Yes, I think we should always keep the XMLResolver.org XML Resolver base version updated.

Great, thanks for confirming. I added mention about the XML resolvers to Update Third-Party Dependencies. Not sure if you have seen that page, but I created it to keep some basic facts/references about various dependencies in one place.