feat(schema): Allow resolvers to validate a schema

[daffl]

This pull request allows to pass a schema to a resolver and if it should also run validation before or after resolving the data:

const userBeforeResolver = resolve<User, typeof context>({
  schema: userSchema,
  validate: 'before',
  properties: {
    name: async (_name, user) => `${user.firstName} ${user.lastName}`
  }
});

This could be done with separate validation and resolver hooks (and still can) but this way makes things more readable in a generated application since resolving and validation usually happen at about the same time.