fix(Ivy): Fix TypedFormGroup<T> not being assignable to FormGroup

Fixes #134

projects/ngx-sub-form/src/lib/ngx-sub-form.types.spec.ts

@@ -0,0 +1,14 @@
+import { FormControl, FormGroup } from '@angular/forms';
+import { TypedFormGroup } from 'ngx-sub-form';
+
+describe(`TypedFormGroup`, () => {
+  it(`should be assignable to the base @angular/forms FormGroup`, () => {
+    let formGroup: FormGroup;
+
+    const typedFormGroup = new FormGroup({ foo: new FormControl() }) as TypedFormGroup<{ foo: true }>;
+
+    formGroup = typedFormGroup;
+
+    expect(true).toBe(true); // this is a type-only test, if the type breaks the test will not compile
+  });
+});

projects/ngx-sub-form/src/lib/ngx-sub-form.types.ts

@@ -8,15 +8,14 @@ export interface OnFormUpdate<FormInterface> {
   onFormUpdate?: (formUpdate: FormUpdate<FormInterface>) => void;
 }
 
-type Omit<T, K> = Pick<T, Exclude<keyof T, K>>;
 type Nullable<T> = T | null;
 
 export type NullableObject<T> = { [P in keyof T]: Nullable<T[P]> };
 
-export type TypedFormGroup<FormInterface> = Omit<FormGroup, 'controls' | 'value'> & {
+export interface TypedFormGroup<FormInterface> extends FormGroup {
   controls: Controls<FormInterface>;
   value: FormInterface;
-};
+}
 
 export type TypedValidatorFn<T> = (formGroup: TypedFormGroup<T>) => ValidationErrors | null;