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"

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}