Play 3.0 compatibility

[russellremple]

Proposed changes

Add Scala 2.13 and Scala 3 artifacts for the play-json version compatible with Play 3.0. (Play 3.0 uses play-json 3.0.)

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

No new tests, just a new set project that runs existing shared weejson tests.

[russellremple]

Since this is a very small change with zero impact to existing artifacts, I'm going to merge it without approvals.