Support react-refresh and shared client/server types (#98)

- Adds support for react-refresh through `@pmmwh/react-refresh-webpack-plugin`. Updated webpack config to support this. Means entire app is no longer refreshed on changes, only individual components, and state is maintained.
- React refresh removes need for `google-apps-script-webpack-dev-server` package
- In client code, support for server function autocomplete through use of gas-client 1.0.0. Requires certain files to be typescript .ts files
- Remove need for "global" exports in main server file through updated gas-webpack-plugin

src/client/dialog-demo/components/SheetEditor.jsx

@@ -4,9 +4,7 @@ import FormInput from './FormInput';
 import SheetButton from './SheetButton';
 
 // This is a wrapper for google.script.run that lets us use promises.
-import server from '../../utils/server';
-
-const { serverFunctions } = server;
+import { serverFunctions } from '../../utils/serverFunctions';
 
 const SheetEditor = () => {
   const [names, setNames] = useState([]);