Provide mechanism to pass attributes to specific widgets

Currently you can pass attributes to widgets via `widget-`, but that passes to all widgets.

This should be refined to pass attributes to specific widgets.

E.g. `widget-checkBox-class`, `widget-datePicker-class`

Start by locating the code that handles the existing `widget-` attributes and how widget names such as `checkBox` and `datePicker` are resolved. Trace the current propagation path, then define the expected behavior for widget-specific keys like `widget-checkBox-class` and verify that attributes no longer apply to unrelated widgets.

Written by the indexing model from the issue text.