While looking at issue #19943 I saw that btn-group for radios is again broken in J4.
I've fixed that previously with #19326, but I think with the PR to separate the layouts that PR got "reverted".
So this PR again reinstates the fix from my previous PR.

Summary of Changes

Adds proper classes to support btn-group behaviours from J3.

Testing Instructions

(copied from original PR)
To test, you can add the following code to the config.xml of any extension. Eg to /administrator/components/com_content/config.xml. Just put it right after the <config> tag.

	<fieldset
		name="test"
		label="Test"
	>
		<field
			name="plain"
			type="radio"
			class=""
			default="1"
		>
			<option value="1">Foo</option>
			<option value="0">Bar</option>
		</field>

		<field
			name="btn-group"
			type="radio"
			class="btn-group"
			default="1"
		>
			<option value="1">Foo</option>
			<option value="0">Bar</option>
		</field>

		<field
			name="btn-group-yesno"
			type="radio"
			class="btn-group btn-group-yesno"
			default="1"
		>
			<option value="1">JYES</option>
			<option value="0">JNO</option>
		</field>

		<field
			name="btn-group-yesno reordered"
			type="radio"
			class="btn-group btn-group-yesno"
			default="1"
		>
			<option value="0">JNO</option>
			<option value="1">JYES</option>
		</field>

		<field
			name="switcher"
			type="radio"
			class="switcher"
			default="1"
		>
			<option value="0">JNO</option>
			<option value="1">JYES</option>
		</field>
	</fieldset>

Now go to the settings of that component. You will have a new tab with 5 parameters.
Check if the radios work.
Make also sure the plain radios and the switcher work as well.

Expected result

All radios work
We even get some styling as expected, but main point is they work ?

Actual result

The marked radios are not working (and styling doesn't exist).