feat: add support for AsEnumCollection casts

[Braunson]

Summary

This adds support for the AsEnumCollection casts. Referenced in the Laravel documentation.

This references #1553

Type of change

• Bug fix (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)
• This change requires a documentation update
• Misc. change (internal, infrastructure, maintenance, etc.)

Checklist

• Existing tests have been adapted and/or new tests have been added
• Add a CHANGELOG.md entry
• Update the README.md
• Code style has been fixed via composer fix-style

[mfn]

Tests are failing.

Please remove any non-code (aka: whitespace) changes.

It helps if you try running the test suite locally

[Braunson]

Just a heads up @mfn the composer fix-style command is what is adding the strict types so I didn't commit any changes from it. If that's in the docs to run, you may want to either accept that change or update the php-cs-fixer rules.

[mfn]

Nice, LGTM!

Thanks regarding the fix-style, wasn't aware!

[barryvdh]

Thanks!