Retain circuit editor when hidden (#2315)

This avoid the delay when switching away from the circuit editor and
then back while it reloads the UX.

Author: billti

vscode/src/circuitEditor.ts

@@ -12,6 +12,7 @@ export class CircuitEditorProvider implements vscode.CustomTextEditorProvider {
     const providerRegistration = vscode.window.registerCustomEditorProvider(
       CircuitEditorProvider.viewType,
       provider,
+      { webviewOptions: { retainContextWhenHidden: true } },
     );
     return providerRegistration;
   }