src/vs/workbench/browser/parts/editor/sideBySideEditor.ts/SideBySideEditor/toEditorViewStateResource
class SideBySideEditor:	protected toEditorViewStateResource(input: EditorInput): URI | undefined {
		let primary: URI | undefined;
		let secondary: URI | undefined;

		if (input instanceof SideBySideEditorInput) {
			primary = input.primary.resource;
			secondary = input.secondary.resource;
		}

		if (!secondary || !primary) {
			return undefined;
		}

		// create a URI that is the Base64 concatenation of original + modified resource
		return URI.from({ scheme: 'sideBySide', path: `${multibyteAwareBtoa(secondary.toString())}${multibyteAwareBtoa(primary.toString())}` });
	}