Consider also using visible text for modal confirm button in confirm_via_gl_modal.js

In ~/lib/utils/confirm_via_gl_modal/confirm_via_gl_modal.js#L6-9 the screen-reader-only text is fetched from the originating button/link. Visible text is ignored, but it's not clear why.

Previous work

• Use custom modal instead of browser confirm (!73167 - merged)
• Replace `window.confirm` in Vue/JS code with `G... (!73950 - merged)