Summary:
Raise an exception with a customised message for two cases when a user tries on operation directly on a table without `.all`:
1. For `Table.Col`, where `Col` is an existing column, suggest `Table.all.Col`. If `Col` doesn't exist as a column, fall back to the standard AttributeError.
2. When iterating directly over a table, e.g. `[r for r in Table]`, suggest looping over `Table.all` instead.
Test Plan: Added Python unit tests.
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D3593
eac1f26f3e