extensions/markdown-language-features/src/markdownEngine.ts/normalizeHighlightLang
function normalizeHighlightLang(lang: string | undefined) {
	switch (lang && lang.toLowerCase()) {
		case 'tsx':
		case 'typescriptreact':
			// Workaround for highlight not supporting tsx: https://github.com/isagalaev/highlight.js/issues/1155
			return 'jsx';

		case 'json5':
		case 'jsonc':
			return 'json';

		case 'c#':
		case 'csharp':
			return 'cs';

		default:
			return lang;
	}
}