TestAddon: Exclude *.stories.* from coverage

[ndelangen]

Closes #29613

What I did

I'm unsure how else to address this issue.
But this fix only addresses the problem when running from storybook, not vitest directly.

The only alternative i can think of would be to change this in the generation.

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[shilman]

Suggested change

	exclude: [...(this.vitest?.config?.coverage?.exclude || []), '**/*.stories.*'],
	exclude: [...(this.vitest?.config?.coverage?.exclude || []), '**/*.stories.*', 'storybook-static'],

[JReinhold]

this.vitest is always going to be undefined at this point, either because this is the first time starting it, or becase a restart always closes vitest first.

So I don't think this is adequate to combine with the user's and/or Vitest's default exclude list.

We need to first resolve the Vitest config, and then we can read from it. The Vitest maintainers have given me a code snippet like this, that should work (maybe with slight modifications):

import { resolveConfig as viteResolveConfig } from 'vite';
import { VitestPlugin, resolveConfig as vitestResolveConfig } from 'vitest/node';

const resolveConfig = async () => {
  const viteConfig = await viteResolveConfig({
    plugins: [VitestPlugin()]
  });
  return vitestResolveConfig(viteConfig);
}