feat: support process and Buffer globals

[markdalgleish]

This is a new feature based on an issue reported against Remix: remix-run/remix#6665

In the linked issue (once the fix in #120 has been applied) the build fails due to a package that assumes the process global is available.

To address this scenario, this PR adds a new globals option to the plugin. In order to make this a non-breaking change, right now it's optional and disabled by default.

I realise there's a few details in this PR that you might want to change, particularly around the API and its surface area, but I thought this would be a good way to start the conversation at least.

Status and versioning classification:

• Code changes have been tested and working fine, or there are no code changes
• This PR changes the library's interface (methods or parameters added)

[imranbarbhuiya]

Thanks, I tested both prs with the repo present in remix issue and some other default exports + non-default exports and it's working