title: how to use custom context in when-clause-contexts matches operator
body: <p>I want to show context menu when right click some path.
  I set when-clause-contexts like this, it worked. (path include somevalue, the context menu shown).</p>
  <pre><code>&quot;when&quot;: &quot;resourcePath =~ /somevalue/&quot;
  </code></pre>
  <p>now I want set value by custom context ,but it not work.</p>
  <p>set context:</p>
  <pre><code>vscode.commands.executeCommand('setContext', 'abc', new RegExp('somevalue'));
  </code></pre>
  <p>when-clause-contexts:</p>
  <pre><code>&quot;resourcePath =~ abc&quot;
  </code></pre>