Form data are completely isolated from their source #9844

Because we will submit form data for mutation, and because we merge the
mutation result back into the form data via
`NaturalAbstractModelService.updateNow()`, then we must make triple-sure
 that the form is not populated with readonly objects coming from our
 API. Otherwise, a structure like the following would raise JS errors
 after mutation:

 ```json
 {
    id: 123,
    name: 'foo',
    product: {
        id: 456,
        quantity: 5, // This used to fail if fetched from mutation
    }
}
 ```

projects/natural/src/lib/services/abstract-model.service.ts

@@ -11,6 +11,7 @@ import {makePlural, mergeOverrideArray, relationsToIds, upperCaseFirstLetter} fr
 import {PaginatedData} from '../classes/data-source';
 import {NaturalDebounceService} from './debounce.service';
 import {ApolloQueryResult} from '@apollo/client/core/types';
+import {deepClone} from '../modules/search/classes/utils';
 
 export type FormValidators = Record<string, ValidatorFn[]>;
 
@@ -143,7 +144,7 @@ export abstract class NaturalAbstractModelService<
      * `getFormGroupValidators`, `getFormGroupAsyncValidators` might be.
      */
     public getFormGroup(model: Literal): UntypedFormGroup {
-        const formConfig = this.getFormConfig(model);
+        const formConfig = this.getFormConfig(deepClone(model));
         return new UntypedFormGroup(formConfig, {
             validators: this.getFormGroupValidators(model),
             asyncValidators: this.getFormGroupAsyncValidators(model),