Add ‘apply theme’ to LVGL widget

[fietser28]

Is your feature request related to a problem? Please describe. No, just a limitation.

Describe the solution you'd like Add the option ‘apply theme’ to the LVGL widget. This needs 2 selections the widget the theme should be applied to and the theme that should be applied. Only the set properties in the style (and parents of the style) should be applied, allowing for changing specific properties.

A common example is to allow for more colors depending on some kind of status/value. E.g. green/yellow/red

Describe alternatives you've considered Currently the selection of themes is limited to states of the widget. In some cases you want to have more possibilities or is doesn’t align with the state (e.g. disabled).

Other option is to have multiple instances of the widget with different styles and show only the one you want. This is very cumbersome and not efficient.

Additional context I’m not sure how to handle widgets inside user widgets:

• Apply to all instances or select a specific instance? Or maybe allow the user to choose by presenting individual instances and the user widget in the dropdownlist.
• if called from within a user widget only widgets in this user widget (and children) should be selectable and when executed it will only apply to this instance.