fix(cloud_firestore): startAfterDocument with where a DocumentReference throws

[agent3bood]

Description

Replace this paragraph with a description of what this PR is doing. If you're modifying existing behavior, describe the existing behavior, how this PR is changing it, and what motivated the change.

Related Issues

closes #10338

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

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• Yes, this is a breaking change.
• No, this is not a breaking change.

The command melos run analyze fails in packages not related to my PR, see bellow.

$ melos exec
  └> dart analyze . --fatal-infos
     └> FAILED (in 4 packages)
        └> cloud_firestore_odm (with exit code 1)
        └> cloud_firestore_odm_example (with exit code 1)
        └> cloud_firestore_odm_generator (with exit code 1)
        └> cloud_firestore_odm_generator_integration_test (with exit code 1)

[Lyokone]

Looks good but tests should be moved to integration testing.

[Lyokone]

Rebased the branch on master to get CI working with Flutter 3.7

[Lyokone]

Thanks for your help :)