src/vs/workbench/services/themes/browser/workbenchThemeService.ts/validateThemeId
function validateThemeId(theme: string): string {
	// migrations
	switch (theme) {
		case VS_LIGHT_THEME: return `vs ${defaultThemeExtensionId}-themes-light_vs-json`;
		case VS_DARK_THEME: return `vs-dark ${defaultThemeExtensionId}-themes-dark_vs-json`;
		case VS_HC_THEME: return `hc-black ${defaultThemeExtensionId}-themes-hc_black-json`;
		case VS_HC_LIGHT_THEME: return `hc-light ${defaultThemeExtensionId}-themes-hc_light-json`;
	}
	return theme;
}