Fix resolveCodeLens calling validateRange on disposed model

[Copilot]

MainThreadLanguageFeatures.resolveCodeLens awaits the extension host's $resolveCodeLens and then calls model.validateRange(result.range). If the editor/model is disposed during the await, this throws Model is disposed!.

• src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts: extend the existing post-await guard to also bail out when the model is disposed.

const result = await this._proxy.$resolveCodeLens(handle, codeLens, token);
if (!result || token.isCancellationRequested || model.isDisposed()) {
    return undefined;
}
return { ...result, range: model.validateRange(result.range) };