Add captureActivityLogs to CSharpExtensionExports

[Copilot]

Adds a programmatic API for capturing C# extension activity logs, similar to the csharp.captureLogs command but designed for API consumers rather than interactive use.

Changes

CSharpExtensionExports API (src/csharpExtensionExports.ts)

• New ActivityLogCapture interface: disposable, exposes getActivityLogs() returning { csharpLog, lspTraceLog, razorLog }
• New captureActivityLogs(): Promise<ActivityLogCapture> on CSharpExtensionExports

Implementation (src/lsptoolshost/activate.ts, src/activateRoslyn.ts)

• createCaptureActivityLogs(languageServer, razorLogger) wires up observers on the module-level _channel/_traceChannel and sets log levels to Trace for the duration of the capture
• Disposing resets all log levels (LSP server, trace client, Razor) back to their original values

Usage

const exports = await vscode.extensions.getExtension('ms-dotnettools.csharp')?.activate();
const capture = await exports.captureActivityLogs();

// ... do work ...

const { csharpLog, lspTraceLog, razorLog } = capture.getActivityLogs();
await capture.dispose(); // restores log levels