Add viteAsset function to retrieve vite assets

[mikestreety]

Saves adding this to each test:

const manifest = JSON.parse(
				readFileSync(path.resolve(process.cwd(), 'html/_assets/vite/.vite/manifest.json'), 'utf8'),
			),
			corePath = `html/_assets/vite/${manifest['app/sites/site_package/Resources/Private/JavaScript/core.js'].file}`;

		await page.setContentAndScriptTag(
			`
				...
			`,
			corePath,
		);

viteAsset function would live in src/utils.ts and be imported and simplify the code:

import {viteAsset} from '`@liquidlight/playwright-framework/utils`;

await page.setContentAndScriptTag(
			`
				...
			`,
			viteAsset('app/sites/site_package/Resources/Private/JavaScript/core.js')
		);