[HxSwitch] Classes form-check form-switch missing

[alexax578]

Resolves: #742

I totally missed the scenario of HxSwitch that is built upon the logic of HxCheckbox. I have adjusted the logic as follows:

• Created a separate property for a CSS class named AdditionalFormElementCssClass which is always applied and allows HxSwitch to apply it's form-switch class.
• Adjusted the structure of the private properties and logic of when and where the form-check CSS class is applied.
• When no Text is present the form-check CSS class should be omitted according to https://getbootstrap.com/docs/5.3/forms/checks-radios/#without-labels

Should contain breaking changes only on the protected API.