Improve CheckboxRadioSwitch for better accessibility

[JuliaKirschenheuter]

As i saw implementation within nextcloud/server#32557 i have noticed, that the accessibility for CheckboxRadioSwitch needs to be improved.

1. Real input should be positioned within the label, on top of the SVG.
   When you hide an interactive element, make sure you choose a hiding technique that keeps it screen reader-accessible, position it on top of whatever is visually replacing it so that a user navigating by touch can find it where they expect to, and then make it transparent.

2. Styles
   https://github.com/nextcloud/nextcloud-vue/blob/d806d43e6b70364e740d8a00d71df46b547b4a7a/src/components/CheckboxRadioSwitch/CheckboxRadioSwitch.vue#L414-L420

should be replaced with

position: absolute
opacity: 0; 
z-index: -1;
// hide it visually but make sure it is still ‘physically’ present where it would naturally be present so that touch users can find it with haptics.
width: 1em;
height: 1em;

see more here https://www.sarasoueidan.com/blog/inclusively-hiding-and-styling-checkboxes-and-radio-buttons/