(core) deal with write access for attachments

Summary:
Attachments are a special case for granular access control. A user is now allowed to read a given attachment if they have read access to a cell containing its id. So when a user writes to a cell in an attachment column, it is important that they can only write the ids of cells to which they have access. This diff allows a user to add an attachment id in a cell if:

  * The user already has access to that a attachment via some existing cell, or
  * The user recently updated the attachment, or
  * The attachment change is from an undo/redo of a previous action attributed to that user

Test Plan: Updated tests

Reviewers: georgegevoian, dsagal

Reviewed By: georgegevoian, dsagal

Differential Revision: https://phab.getgrist.com/D3681

app/common/GranularAccessClause.ts

@@ -46,6 +46,7 @@ export interface UserInfo {
   LinkKey: Record<string, string | undefined>;
   UserID: number | null;
   UserRef: string | null;
+  SessionID: string | null;
   [attributes: string]: unknown;
   toJSON(): {[key: string]: any};
 }