Strip Markdown when announcing chat input notification to screen readers

[dmitrivMS]

Follow-up to #315360 (review comment from Copilot on the merged PR).

active.message can be an IMarkdownString (e.g. the agent-host permission notification wraps paths in backticks). The previous fix passed .value straight to aria.status(...), so screen readers would read Markdown syntax — backticks, link targets, etc. — verbatim.

This PR:

• Imports renderAsPlaintext from vs/base/browser/markdownRenderer and uses it to strip Markdown before announcing.
• Keeps the dedupe signature based on the raw .value, which is cheap to compute, and only renders the plaintext after the signature check passes — so we don't pay the parse cost on unrelated onDidChange fires.

Verified: Core - Typecheck task reports Finished compilation with 0 errors.

[meganrogge]

thank you!

[Copilot]

Pull request overview

This PR improves screen reader announcements for chat input notifications by ensuring notifications backed by IMarkdownString are converted to plaintext before being sent to aria.status(...), preventing Markdown syntax (backticks, link markup, etc.) from being read aloud.

Changes:

• Import renderAsPlaintext from vs/base/browser/markdownRenderer.
• Keep the dedupe signature computed from the raw .value (cheap), and only compute plaintext after the dedupe check passes.
• Announce the plaintext-rendered notification message (plus optional description) via status(...).

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/browser/widget/input/chatInputNotificationService.ts	Convert IMarkdownString notification messages to plaintext before ARIA announcement, while preserving efficient deduping.

Copilot's findings

• Files reviewed: 1/1 changed files
• Comments generated: 0