Added basic test cases to donut chart

[v-baambati]

Added basic test cases to donut chart and horizontalbar chart

[krkshitij]

Does the page render all donut-chart stories by default? We should have separate examples for testing to avoid modifying the test file whenever the stories change.

See this:

fluentui/packages/web-components/src/accordion/accordion.spec.ts

Lines 21 to 32 in e32acb8

	await page.setContent(/* html */ `
	<fluent-accordion expand-mode="multi">
	<fluent-accordion-item>
	<span slot="heading">Heading 1</span>
	<div>Content 1</div>
	</fluent-accordion-item>
	<fluent-accordion-item>
	<span slot="heading">Heading 2</span>
	<div>Content 2</div>
	</fluent-accordion-item>
	</fluent-accordion>
	`);

[v-baambati]

For now added test cases on existing example which is there in the stories.