feat: add Imperaitive Handle to public API

[Caele]

Motivation

Exposes the Imperative handle API in the form of

• useImperativeHandle component hook
• getimperativeHandle viz API function

Requirements checklist

• Api specification
  • Ran yarn spec
    • No changes OR API changes has been formally approved
• Unit/Component test coverage
• Correct PR title for the changes (fix, chore, feat)

When build and tests have passed:

• Add code reviewers, for example @qlik-oss/nebula-core

[T-Wizard]

maybe simplify to

Suggested change

	* @template T
	* @param {function():T} factory
	* @param {function():object} factory

The generic type T don't give any value

[Caele]

hmm, you could have the handle function return whatever you want, shouldn't it be the generic type then? Not sure how a TS setup handles it?

[T-Wizard]

as this is the only place where the type is referenced I don't think it gives any value.
(but I also don't there is any real problem with keeping it as it is)

[veinfors]

Looks good to me.
A good idea is to test this change with some existing charts where the useImperativeHandle hook is used already, like the sn-bar-chart, sn-pie-chart etc. to make sure we don't break anything for existing extensions.

[Caele]

Looks good to me. A good idea is to test this change with some existing charts where the useImperativeHandle hook is used already, like the sn-bar-chart, sn-pie-chart etc. to make sure we don't break anything for existing extensions.

There shouldn't be any functional changes, only typings are added and the API exposed to mashups.