Fix missed Previewer.plain call due to adjacent @ts-expect-error

[andrewbranch]

I used a // @ts-expect-error until 4.3 protocol update comment in some completions code in #119009, but it unintentionally silenced an error that should have arisen as part of @mjbvz’s refactor in #119358. I’ve fixed that, and also shuffled some of the remaining temporary // @ts-expect-error comments to target less code.

I also wrote a smoke test to add to completions.test.ts, but I’m not sure how to run it (without running all smoke tests), and I have low confidence I wrote it correctly, so I haven’t committed it yet. But the content is

test('Import statement completions should work', async () => {
	await createTestEditor(vscode.Uri.parse('/node_modules/styled-components/index.d.ts'),
		`export declare function styled(): any;`
	);

	const indexUri = vscode.Uri.parse('/index.ts');
	const editor = await createTestEditor(indexUri,
		`import sty`
	);

	await acceptFirstSuggestion(indexUri, _disposables);

	assertEditorContents(editor, `import { styled } from "styled-components";`);
});

I also suppose this won’t work until smoke tests are run against TypeScript 4.3, and I’m not sure how that works either.

[mjbvz]

Thanks! Will follow up on the test once we pick up TS 4.3