feat(ui5-switch): add required property

[hinzzx]

Introducing the required property for the Switch control.
We now also enable the Form Support feature within the control, which means now the Switch component, could be easily used and integrated within forms as well.

Fixes: #5897

[nnaydenow]

Please also check what would be the bevahiour of the newly added property inside following scenario: #7319 (please rework it to work in your case by replacing ui5-checkbox with ui5-switch)

[unazko]

According to the screen reader announcements and attributes all seems to be working fine.
About the form support I'll check as well.

[unazko]

I'm fine with the change.

[nnaydenow]

Add test test validates the scenario in a form. You can use html like:

	<form id="switchForm">
		<ui5-switch id="switch1" checked></ui5-switch>
		<ui5-switch id="switch2" required></ui5-switch>
		<br><br>
		<ui5-button id="switchSubmit" type="Submit">Submit</ui5-button>
	</form>

And you can check how formElement.checkValidity() method works and maybe you can add it into the test