Suggestion: Add rich text capabilities to `DragValue`

[Daniikk1012]

I recently discovered that there is no easy way of creating a DragValue where the suffix is grayed out. It is useful to highlight what the actual numeric value is, and what is just the unit.

It should be possible to solve this by incorporating rich text in DragValue, perhaps by adding a custom_layouter method, or making prefix and suffix accept Into<WidgetText> like Button.

For now, the solution seems to be either to use a TextEdit, which you will no longer be able to drag, or implement your own DragValue, which is a lot of work to do.