fix: post hook 'res' param with type any

[GCastilho]

-- Fix post hook using PostMiddlewareFunction generic type without passing T to ResType

Summary

The type for the 'post hook' middleware is passing the T only to the first argument of the PostMiddlewareFunction (the this type), not to the second, resulting on the ResType defaulting to any

Examples

type User = {
  name: string
}
const userSchema = new Schema<User>({ ... })

# Before
userSchema.post('validate', (doc, next) => {
  // doc has type 'any'
})

# After
userSchema.post('validate', (doc, next) => {
  // doc has type 'User'
})

[Uzlopak]

Can you add some typings tests please?

[GCastilho]

@Uzlopak I've added some tests for the types. Please let me know if you think it needs more or if there is a problem with them

[Uzlopak]

LGTM

[vkarpov15]

In principle this looks ok, but the TS benchmark results don't look so good. Although I suspect they may be better after #11925 .

[vkarpov15]

I'll approve and merge this for now, so I can double check the TypeScript benchmark. PR looks good pending benchmark results.

[GCastilho]

Thank you :D