docs(combobox): remove separate tab focus for nested pickerbutton (#3507)

The Picker Button that is nested within Combobox was previously tab
focusable, separately from the Combobox itself. This update gives it
a negative tabindex, making it consistent with the intended behavior
and SWC implementation.

This adds a tabindex option to the Picker Button template.

Author: jawinn

components/combobox/stories/template.js

@@ -89,6 +89,7 @@ const Combobox = ({
 				onclick: function () {
 					updateArgs({ isOpen: !isOpen });
 				},
+				tabindex: "-1",
 			}, context)}
 		</div>
 	`;

components/pickerbutton/stories/template.js

@@ -25,6 +25,7 @@ export const Template = ({
 	isRounded = false,
 	customStyles = {},
 	onclick,
+	tabindex,
 } = {}, context = {}) => {
 	const { updateArgs } = context;
 
@@ -54,6 +55,7 @@ export const Template = ({
 				if (isDisabled) return;
 				updateArgs({ isOpen: !isOpen });
 			}}
+			tabindex=${ifDefined(tabindex)}
 		>
 			<div class="${rootClass}-fill">
 				${when(label, () => html`