feat: add schema extensions

[runspired]

This PR still requires more tests.

Implements the idea in #10029 which should allow us to bake an api-compatible version of ModelFragments directly into SchemaRecord rather rapidly

• adds ember-object and ember-array-like extensions for arrays
• adds ember-object extension for objects

Tests:

Object Via Field

• [ ] computed
• [ ] cached
• [ ] getter
• [ ] method

SchemaObject Via Field

• [ ] method

SchemaObject Via SchemaArrayField

• [ ] method

SchemaObject Via Resource

• [ ] method

SchemaObject Via Field & Resource

• [ ] method

Resource

• [ ] method

Array

• [ ] getter
• [ ] method

SchemaArray

• [x] getter
• [x] method

ManyArray

• [ ] getter
• [ ] method