Optimize closeActiveWindows to reduce likelihood of test timeouts resulting in CI failures

[DonJayamanne]

Currently we have a few timeouts when invoking VSC API to close documents.
Possible improvements:

• Invoke workbench.action.closeAllEditors with a very short timeout (1s)
• Check if any documents are opened before invoking this
• Attempt to close the active editor before invoking this
• Iterate through editors, show the document one by one and close the docs
• Finally attempt workbench.action.closeAllEditors with the 15s timeout.

The code is as follows:

export async function closeActiveWindows(): Promise<void> {
    return new Promise<void>((resolve, reject) => {
        vscode.commands.executeCommand('workbench.action.closeAllEditors')
            // tslint:disable-next-line:no-unnecessary-callback-wrapper
            .then(() => resolve(), reject);
        // Attempt to fix #1301.
        // Lets not waste too much time.
        setTimeout(() => {
            reject(new Error('Command \'workbench.action.closeAllEditors\' timed out'));
        }, 15000);
    });
}