theme provider for sap-theming-base-content

[hardl]

Luigi has a high level theme handling mechanism, allowing to manage theme information and propagate it to the micro frontends. What luigi doesn't do is to actually apply a theme at the core app, after it is selected. Goal of this issue is to provide an easy way of applying a theme in a system that is using Fiori3 in order to avoid boilerplate implementations at our customers.