Simplify submenu disclosure button label

I agree that More {{ item.title }} pages is a verbose, despite it matching the Example Disclosure Navigation Menu with Top-Level Links pattern on w3.org.

It looks like Olivero's submenu toggle is using "Toggle sub-navigation". I don't like that at all. I don't really like "sub-navigation" or "submenu," both feel very jargony to me. I'm inclined to recommend {{ item.title }} pages, but I worry that will be verbose too unless the link title is very short. Something like: "Admission & Aid pages" feels like a lot and considering screen readers would process the menu like "Admission & Aid, Admission & Aid pages" which really feels like a mouthful.

I wonder if More {{ item.title }} is a reasonable compromise even though we'd need to swap to Less {{ item.title }} while it was toggled open.

Updated the button label to "Submenu for LINK_TITLE" and set the default value for the visible label (if enabled) to the same.

I looked into this more, got some advice from the a11y slack and was referred to this article: https://adrianroselli.com/2019/06/link-disclosure-widget-navigation.html....

Based on this a good approach is to use aria-labelledby and reference the link text instead of adding extra hidden text. Aria-expanded already gives context about what the button does, and this is less verbose for screen reader users

<a id="about" href="/about">About</a>
<button aria-labelledby="about" ...></button>