**Description of the issue/feature this PR addresses:**

When adding a custom field (e.g., via Studio) to the Documents list view, clicking the cell directly does not trigger inline edit mode. The user has to first click a standard editable field (like "Owner") to put the row into edit mode before they can modify the custom field.

This occurs because we use a hardcoded whitelist (`editableColumns`) of standard fields allowed to trigger edit mode. Custom fields (`x_`) are missing from this static list.

This commit resolves the issue by dynamically injecting visible, non-readonly custom fields into the `editableColumns` whitelist. This allows user-created fields to be edited inline as expected.

**Steps to reproduce:**

- Documents > Studio > List view > Add any field that accepts user input (e.g. Text/char) > save/exit
- In the same Documents list view > select a row > click the cell belonging to the newly created field > observe that the row does not enter edit mode
- In the same Documents list view > select a row > click a standard editable cell, then click the cell belonging to our newly created field > observe that this then allows us to edit our field


**Current behavior before PR:**

- Custom fields do not trigger inline edit mode

**Desired behavior after PR is merged:**

- Custom fields trigger inline edit mode

opw-6378102