Replace is_tombstone with removal timestamp

Author: link2xt

src/sql/migrations.rs

@@ -1140,11 +1140,17 @@ CREATE INDEX msgs_status_updates_index2 ON msgs_status_updates (uid);
 
     inc_and_check(&mut migration_version, 128)?;
     if dbversion < migration_version {
+        // Add the timestamp of addition and removal.
+        //
+        // If `add_timestamp >= remove_timestamp`,
+        // then the member is currently a member of the chat.
+        // If `add_timestamp < remove_timestamp`,
+        // then the member is a past member.
         sql.execute_migration(
             "ALTER TABLE chats_contacts
-             ADD COLUMN timestamp NOT NULL DEFAULT 0;
+             ADD COLUMN add_timestamp NOT NULL DEFAULT 0;
              ALTER TABLE chats_contacts
-             ADD COLUMN is_tombstone NOT NULL DEFAULT FALSE;
+             ADD COLUMN remove_timestamp NOT NULL DEFAULT 0;
             ",
             migration_version,
         )