Feauture request: allow user to set how to detect subject type

[ppodds]

Users are not allowed to set how to detect subject type when they are building abilities. It may cause the wrong subject type detection and get an unpredictable result.

casl docs

e.g.

it('test', async () => {
  expect(accessService.hasAbility(user, Actions.delete, new Post())).toBeTruthy(); // not pass
});

The test above would not pass but can be solved by the below solutions.

ability.factory.ts

...
// For PureAbility skip conditions check, conditions will be available for filtering through @CaslConditions() param
if (abilityClass === PureAbility) {
  return ability.build({ conditionsMatcher: nullConditionsMatcher, detectSubjectType: object => object.constructor as ExtractSubjectType<Subjects> });
}
return ability.build({ detectSubjectType: object => object.constructor as ExtractSubjectType<Subjects> });

or

it('test', async () => {
  const post = new Post();
  expect(accessService.hasAbility(user, Actions.delete, subject(post.constructor as any, post))).toBeTruthy(); // pass
});

[belgamo]

In addition to that, can we update the library to support string as the subject type? CASL by nature supports that. Currently, this library only accepts class types, making typescript complain when providing string types, although the code works.

[belgamo]

Here is a practical example of what I mean. I had to cast the string to make TS stop complaining