add telemetry on thinking styles

[justschen]

adds telemetry tracking for our setting

[Copilot]

Pull request overview

Adds telemetry in the Chat widget to record which “thinking style” rendering mode is in use when sending or rerunning a chat request, so usage can be analyzed across chat entry points/locations.

Changes:

• Introduces a new chat.thinkingStyleUsage telemetry event (thinkingStyle, location, requestKind).
• Logs the event on request submit and on rerun of the last request.
• Adds a small helper to sanitize/normalize the configured thinking style before logging.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts:2438

• Telemetry for chat.thinkingStyleUsage is logged immediately after sendRequest(...) returns a non-rejected ChatSendResult, but before awaiting the queued result (result.deferred) and confirming ChatSendResult.isSent(sent). If a request is queued and later not sent (or fails), this will still emit a usage event. Move this log to after the isSent check so the event only fires for actually-sent requests.

		this.logThinkingStyleUsage('submit');

		// visibility sync before firing events to hide the welcome view
		this.updateChatViewVisibility();
		this.input.acceptInput(options?.storeToHistory ?? isUserQuery);

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