Provide screen reader feedback when Views List is filtered by name or description

Problem/Motivation

The Views listing page (admin/structure/views offers a text input to filter Views by name or description. When entering text, the list of views changes dynamically. The change is easily noted visually, but is not conveyed to users with screen readers.

Proposed resolution

Use Drupal.announce() to convey a short message about the number of views now present in the filtered list.

We already do this with the module filter on the admin/modules page - see system.modules.js.

A difference with the Views listing is that there are actually TWO listings on the page: enabled and disabled views. So it may be worth announcing the count for each listing.

Remaining tasks

• Devise the announcement string(s); e.g. "1 enabled view and 2 disabled views are available in the modified list." It should handle singular/plural result counts correctly (with Drupal.formatPlural())
• Write a patch.
• Tests - confirm the updated content of div#drupal-live-announce with JavascriptTestBase.

User interface changes

• No visible changes intended.
• Add a screen reader announcement to convey updates which are currently only apparent visually.
• Introduces a new translatable string for Drupal.announce().

API changes

None expected.

Data model changes

None expected.