Add context menu to set cell value to NULL

[seancolsen]

Current behavior

The user has no way to set a cell value to NULL.

Desired behavior

1. Right click within a cell (or click-hold on a touch device).
2. The browser's native context menu is suppressed.
3. The cell is selected.
4. A Mathesar-specific context menu appears.
5. An item exists within the context menu labeled "Set to NULL".
6. The menu entry is disabled if any of the following conditions are met:
   • The value is already NULL.
   • The column does not allow NULL.
7. After the user clicks on the menu entry, the context menu disappears and Mathesar exhibits the same loading, success, and error behavior as when updating a value within a cell via typing new text and pressing Enter.

Notes

• faBackspace, or faTimes would probably be acceptable icons to use in the menu.

Additional context

• See NULL Value Specs, scenario 3a

See also

• Add keyboard shortcuts for setting a cell to NULL #936

Status

• Blocked by Create Menu component #742, especially because we should rely on DropdownMenu functionality to implement the disabled feature.

[seancolsen]

@ghislaineguerin the specs require the context menu entry to be "Set as NULL". That wording seems a bit awkward. Can we use "Set to NULL" instead?

[kgodey]

@seancolsen I think it's fine to use "Set to NULL".

[seancolsen]

Thanks @kgodey I've updated the issue description to reflect that adjustment.