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/utils/serverFunctions.ts

@@ -0,0 +1,10 @@
+import { GASClient } from 'gas-client';
+import * as publicServerFunctions from '../../server';
+
+const { serverFunctions } = new GASClient<typeof publicServerFunctions>({
+  // this is necessary for local development but will be ignored in production
+  allowedDevelopmentDomains: origin =>
+    /https:\/\/.*\.googleusercontent\.com$/.test(origin),
+});
+
+export { serverFunctions };