(core) Add /attachments/updateUsed DocApi endpoint to soft delete all unused attachments in document

Summary:
Builds on https://phab.getgrist.com/D3352

Add DocStorage.scanAttachmentsForUsageChanges to do fancy JSON query to find all attachment metadata rows whose soft deletion status needs updating.

Add ActiveDoc.updateUsedAttachments which uses the above and then applies the appropriate user action if needed to soft delete/undelete metadata rows.

Add endpoint in DocApi calling ActiveDoc method.

Test Plan: Added DocApi test

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3357

app/server/lib/DocApi.ts

@@ -230,6 +230,12 @@ export class DocWorkerApi {
         .send(fileData);
     }));
 
+    // Mostly for testing
+    this._app.post('/api/docs/:docId/attachments/updateUsed', canEdit, withDoc(async (activeDoc, req, res) => {
+      await activeDoc.updateUsedAttachments();
+      res.json(null);
+    }));
+
     // Adds records given in a column oriented format,
     // returns an array of row IDs
     this._app.post('/api/docs/:docId/tables/:tableId/data', canEdit,