Address review feedback on databinding whitelist characterization spec

[borinquenkid]

Stacked on #16003.

Addresses review comments from @jdaugherty:

• Renames the Object-typed field to untypedProperty and rewords test names — the property is excluded because it is raw Object-typed (DefaultASTDatabindingHelper#shouldFieldBeInWhiteList), not because it is generically "unlisted".
• Drops the misleading hasOne association, which added nothing to the tested contract and declares an incomplete mapping (no belongsTo back-reference on WhitelistAddress).
• Trims the domain test to its non-duplicated assertions and cross-references DefaultASTDatabindingHelperDomainClassSpecialPropertiesSpec, which already pins id/version/dateCreated/lastUpdated exclusion for domain classes.

Verification

• :grails-test-suite-web:test --tests DefaultDatabindingWhitelistBehaviorSpec
• ./gradlew codeStyle

[Copilot]

Pull request overview

This PR updates the DefaultDatabindingWhitelistBehaviorSpec test to better characterize the databinding allowlist contract by clarifying why certain properties are excluded (raw Object/def typing) and by removing unrelated/duplicative assertions from the domain portion of the test.

Changes:

• Renamed the previously “ignored” Object property to untypedProperty and updated test descriptions to reflect the actual exclusion rule.
• Simplified the domain binding scenario by dropping special-property assertions and an unnecessary/misleading hasOne association mapping.
• Added an inline cross-reference to the existing spec that already pins domain special-property exclusions.

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[borinquenkid]

Folding this directly into #16003 instead — no need for a separate stacked PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.1147%. Comparing base (23f7c46) to head (1c34ff0).
⚠️ Report is 1 commits behind head on test/databinding-codegen-contract.

Additional details and impacted files

@@                             Coverage Diff                             @@
##             test/databinding-codegen-contract     #16054        +/-   ##
===========================================================================
- Coverage                              51.1210%   51.1147%   -0.0063%     
  Complexity                               17600      17600                
===========================================================================
  Files                                     2041       2041                
  Lines                                    95493      95493                
  Branches                                 16587      16587                
===========================================================================
- Hits                                     48817      48811         -6     
- Misses                                   39390      39399         +9     
+ Partials                                  7286       7283         -3     

see 4 files with indirect coverage changes

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