Support customised service loader

[nicobrevin]

Description of Changes

As per #1382, adds a custom ServiceLoader#load method that supports customizing the classloader. In our case we have something of a plugin architecture that isolates the different plugins in their own class loader. This causes chaos and hilarity when the netcdf plugin is used, as it is not going to execute that code with the netcdf library's classloader set as the calling thread's context classloader. I have worked around it to some extent by finaggling our code to do a best-effort and forcibly load some of the offending netcdf classes with the context class loader set correctly, but that only works for the code that loads services in a static initializer.

PR Checklist

• Link to any issues that the PR addresses
• Add labels
• Open as a draft PR
  until ready for review
• Make sure GitHub tests pass
• Mark PR as "Ready for Review"

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[lesserwhirls]

It looks like switching out org.slf4j.LoggerFactory for ucar.nc2.util.log.LoggerFactory broke compilation.

[nicobrevin]

Whoops, fixed. Also ran spotless, but all that did was remove some whitespace from my javadoc 🤷

If you think the change needs it, I can add tests, but I gave up quickly when I got errors about missing JDKs.

[lesserwhirls]

I think this approach will work nicely. Thank you so much for your contribution, @nicobrevin! Besides the compilation issue (see above) and the CLA, the only other thing that's tripping up the GitHub tests is the code style. To check the code style, you can run ./gradlew spotlessCheck, and to apply frixes you can run ./gradlew spotlessApply. Once the github tests pass, I'll run our full set of tests on our internal Jenkins just to be safe. At that point, we should be good to go and this would get in for the 5.10.0 release.