Accept json at populate function

Feature Card

Description

Right now populate function just accepts a Response as an argument and it’d be great to accept a json too.

User Stories

As a Frontity developer
I want to pass a json to populate function
so that I can populate the state the same way as Frontity does for my custom needs

Possible solution

We could add a parameter to populate function named json and if it is passed, ignored the Response.json().