Portable stories: Refactor Storybook preview and Portable stories to reuse logic [kasper]

[yannbf]

We mimic the run of the story in portable stories, but don’t reuse the same code for the story run. We should do that, see this TODO:

storybook/code/core/src/preview-api/modules/store/csf/portable-stories.ts

Lines 326 to 331 in a52726f

	// TODO At some point this function should live in prepareStory and become the core of StoryRender.render as well.
	// Will make a follow up PR for that
	async function playStory<TRenderer extends Renderer>(
	story: PreparedStory<TRenderer>,
	context: StoryContext<TRenderer>
	) {