Provide "setThemeVariants" for HasThemeVariant

[stefanuebe]

Describe your motivation

This is a pure dx improvement / core readability request.

1. To override the current theme variants, it is necessary to remove them manually first and then add a new one (if one wants to use theme variants):

button.removeThemeNames(button.getThemeNames().toArray(String[]::new))
button.addThemeVariants(ButtonVariant.LUMO_PRIMARY);

2. To apply/remove a theme variant to/from a component depending on a boolean, it is necessary to create an if-else like

if (someCondition) {              
    button.removeThemeVariants(ButtonVariant.LUMO_PRIMARY);
} else {
    button.addThemeVariants(ButtonVariant.LUMO_PRIMARY);
}

Both use cases add unnecessary overhead and at least the 1 case is not really intuitive.

Describe the solution you'd like

Please provide a setThemeVariants method similar to the setThemeName(String, boolean) variant,

something like setThemeVariants(Variants...) (use case 1) and setThemeVariants(boolean , Variants...) (use case 2).

Describe alternatives you've considered

See the snippets.

Additional context

No response