feat(ScreenObtainer) add fallback option for Electron

If the enclosing Jitsi Meet app declares gDM in Electron is supported,
ignore the `electronUseGetDisplayMedia` config flag and use the gDM
flow. This facilitates having backwards compatibility since the Electron
app won't know if the deployment it's about to join has the gDM flow
support or not.

modules/RTC/ScreenObtainer.js

@@ -94,7 +94,12 @@ const ScreenObtainer = {
      * @param {Object} options - Optional parameters.
      */
     obtainScreenOnElectron(onSuccess, onFailure, options = {}) {
-        if (window.JitsiMeetScreenObtainer && window.JitsiMeetScreenObtainer.openDesktopPicker) {
+        if (typeof window.JitsiMeetScreenObtainer?.openDesktopPicker === 'function') {
+            // Detect if we have the fallback option.
+            if (window.JitsiMeetScreenObtainer?.gDMSupported) {
+                return this.obtainScreenFromGetDisplayMedia(onSuccess, onFailure);
+            }
+
             const { desktopSharingFrameRate, desktopSharingResolution, desktopSharingSources } = this.options;
 
             window.JitsiMeetScreenObtainer.openDesktopPicker(