(core) Adding google drive plugin as a fallback for url plugin

Summary:
When importing from url, user types a url for google spreadsheet,
Grist will switch to Google Drive plugin to allow user to choose file manualy.

Test Plan: Browser tests

Reviewers: paulfitz, dsagal

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2945

app/client/lib/uploads.ts

@@ -154,6 +154,12 @@ export async function uploadFiles(
 export async function fetchURL(
   docComm: DocComm, url: string, onProgress: ProgressCB = noop
   ): Promise<UploadResult> {
+
+  if (isDriveUrl(url)) {
+    // don't download from google drive, immediately fallback to server side.
+    return docComm.fetchURL(url);
+  }
+
   let response: Response;
   try {
     response = await window.fetch(url);
@@ -173,6 +179,12 @@ export async function fetchURL(
   return res!;
 }
 
+export function isDriveUrl(url: string) {
+  if (!url) { return null; }
+  const match = /^https:\/\/(docs|drive).google.com\/(spreadsheets|file)\/d\/([^/]*)/i.exec(url);
+  return !!match;
+}
+
 /**
  * Convert a form to a JSON-stringifiable object, ignoring any File fields.
  */