Remove DataObjectInterface

[emteknetnz]

DataObjectInterface is a pointless interface that only implements a tiny proportion of DataObjects API

Acceptance criteria

• DataObjectInterface is removed
• Any code that references DataObjectInterface is updated

CMS 5 PRs

• DOC Deprecate DataObjectInterface developer-docs#688
• API Deprecate DataObjectInterface #11605

After merging assign back to Steve to merge-up and rebase

CMS 6 kitchen sink CI

• https://github.com/creative-commoners/recipe-kitchen-sink/actions/runs/13276163366

^ Unit test failure is unrelated - will be fixed by silverstripe/silverstripe-asset-admin#1542
! However behat test in not unrelated

CMS 6 PRs

• API Remove DataObjectInterface silverstripe-elemental#1315
• API Remove DataObjectInterface #11606
• API Remove DataObjectInterface silverstripe-frameworktest#227
• API Remove DataObjectInterface silverstripe-graphql#625
• API Remove DataObjectInterface silverstripe-tagfield#318
• API Remove DataObjectInterface symbiote/silverstripe-gridfieldextensions#427
• API Remove DataObjectInterface tractorcow-farm/silverstripe-fluent#926

[emteknetnz]

Not proceeding as ArbitraryDataModel in frameworktest, which was intended to simulate using GridField as an intermediary to manage third API data (read and write), highlighted the fact that DataObjectInterface does have a purpose, it's just badly named. It should be called something more along the lines of 'WritableDataInterface' as it's not DataObject specific.

This work also highlighed that setCastedField() is poorly named, it really just be rolled into setField() or probably better simply setValue()