feat(multi-stream) Enable multi-stream by default (if not disabled explicitly) (#2116)

* feat(multi-stream) Enable multi-stream by default (if not disabled explicitly).

JitsiMeetJS.js

     init(options = {}) {
         Settings.init(options.externalStorage);
         Statistics.init(options);
+        const flags = options.flags || {};
 
         // Multi-stream is supported only on endpoints running in Unified plan mode and the flag to disable unified
         // plan also needs to be taken into consideration.
-        if (typeof options.enableUnifiedOnChrome !== 'undefined' && options.flags) {
-            options.flags.enableUnifiedOnChrome = options.enableUnifiedOnChrome;
+        if (typeof options.enableUnifiedOnChrome !== 'undefined') {
+            flags.enableUnifiedOnChrome = options.enableUnifiedOnChrome;
         }
 
         // Configure the feature flags.
-        FeatureFlags.init(options.flags || { });
+        FeatureFlags.init(flags);
 
         // Initialize global window.connectionTimes
         // FIXME do not use 'window'

modules/flags/FeatureFlags.js

      * @param {boolean} flags.receiveMultipleVideoStreams - Signal support for receiving multiple video streams.
      */
     init(flags) {
+        this._receiveMultipleVideoStreams = flags.receiveMultipleVideoStreams ?? true;
         this._runInLiteMode = Boolean(flags.runInLiteMode);
-
-        this._sourceNameSignaling = Boolean(flags.sourceNameSignaling);
-        this._receiveMultipleVideoStreams = Boolean(flags.receiveMultipleVideoStreams);
-        this._sendMultipleVideoStreams = Boolean(flags.sendMultipleVideoStreams);
-        this._ssrcRewriting = Boolean(flags.ssrcRewritingOnBridgeSupported);
+        this._sendMultipleVideoStreams = flags.sendMultipleVideoStreams ?? true;
+        this._sourceNameSignaling = flags.sourceNameSignaling ?? true;
+        this._ssrcRewriting = Boolean(flags.ssrcRewritingEnabled);
 
         // For Chromium, check if Unified plan is enabled.
         this._usesUnifiedPlan = browser.supportsUnifiedPlan()
 
         logger.info(`Source name signaling: ${this._sourceNameSignaling},`
             + ` Send multiple video streams: ${this._sendMultipleVideoStreams},`
-            + ` SSRC rewriting supported: ${this._ssrcRewriting},`
             + ` uses Unified plan: ${this._usesUnifiedPlan}`);
     }
 

modules/sdp/LocalSdpMunger.spec.js

     const localEndpointId = 'sRdpsdg';
 
     beforeEach(() => {
-        FeatureFlags.init({ });
+        FeatureFlags.init({ sourceNameSignaling: false });
         localSdpMunger = new LocalSdpMunger(tpc, localEndpointId);
     });
     describe('dontStripSsrcs', () => {
                 expect(videoSsrcs.length).toEqual(6);
             });
             it('with source name signaling enabled (injected source name)', () => {
-                FeatureFlags.init({ sourceNameSignaling: true });
+                FeatureFlags.init({ });
                 transformStreamIdentifiers();
 
                 expect(audioSsrcs.length).toEqual(4 + 1 /* injected source name */);
     const localEndpointId = 'sRdpsdg';
 
     beforeEach(() => {
-        FeatureFlags.init({ });
+        FeatureFlags.init({ sourceNameSignaling: false });
         localSdpMunger = new LocalSdpMunger(tpc, localEndpointId);
     });
     describe('stripSsrcs', () => {
                 expect(videoSsrcs.length).toEqual(1);
             });
             it('with source name signaling', () => {
-                FeatureFlags.init({ sourceNameSignaling: true });
+                FeatureFlags.init({ });
                 transformStreamIdentifiers();
 
                 expect(audioSsrcs.length).toEqual(1 + 1 /* injected source name */);
     });
 
     it('should transform', () => {
-        FeatureFlags.init({ sourceNameSignaling: true });
+        FeatureFlags.init({ });
         transformStreamIdentifiers();
 
         expect(audioMsid).toBe('sRdpsdg-audio-0-1');
     const localSdpMunger = new LocalSdpMunger(tpc, localEndpointId);
 
     it('should not increment track index for new tracks', () => {
-        FeatureFlags.init({ sourceNameSignaling: true });
+        FeatureFlags.init({ });
 
         sdpStr = transform.write(SampleSdpStrings.simulcastRtxSdp);
         desc = new RTCSessionDescription({

types/auto/modules/flags/FeatureFlags.d.ts

      * @param {boolean} flags.receiveMultipleVideoStreams - Signal support for receiving multiple video streams.
      */
     init(flags: any): void;
+    _receiveMultipleVideoStreams: any;
     _runInLiteMode: boolean;
-    _sourceNameSignaling: boolean;
-    _receiveMultipleVideoStreams: boolean;
-    _sendMultipleVideoStreams: boolean;
+    _sendMultipleVideoStreams: any;
+    _sourceNameSignaling: any;
     _ssrcRewriting: boolean;
     _usesUnifiedPlan: any;
     /**