Debounce search results live region and remove “updating” messages

[knowler]

The existing live region on the search result page needs a few improvements for screen reader users:

1. We should debounce the live region updates to avoid both clobbering other messages and spamming screen reader users. After an input change if we can delay the live region updates by 250ms on desktop and around 700ms on mobile that would likely improve the experience for screen reader users in both situations.
2. We don’t need to include “Updating” in the live region for the search results page. This is just extra noise.

Thank you to James Scholes for the feedback here.

[RYGRIT]

Hi @knowler, I've created a PR for this, and I hope you can spare some of your valuable time to review it.