Add screen reader support to the workspace search plugin

[microbit-robert]

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Component

WorkspaceSearch

Problem

This plugin has keyboard navigation, but doesn't have screen reader support yet.

Request

Add support for screen readers that describes:

• How workspace search works (e.g., it is currently esc to focus the found block and this is not obvious)
• Announce when matching blocks are found (perhaps we have to announce the currently matching block - unclear)
• Is focusing the found block when the user presses Esc enough to understand that the workspace search input has closed and focus has now moved to the block you searched for?

Alternatives considered

No response

Additional context

No response