feat: Adds a method that finds the SSRC of a JitsiTrack (#1338)

Adds a JitsiConference.getSsrcByTrack() method that finds the SSRC of a JitsiTrack by its SSRC. This method is currently used to get (and display) the first audio/video SSRC in the GSM popover in Jitsi Meet.

Co-authored-by: George Politis <gp@jitsi.org>

JitsiConference.js

     return this.statistics.isCallstatsEnabled();
 };
 
+/**
+ * Finds the SSRC of a given track
+ *
+ * @param track
+ * @returns {number|undefined} the SSRC of the specificed track, otherwise undefined.
+ */
+JitsiConference.prototype.getSsrcByTrack = function(track) {
+    return track.isLocal() ? this.getActivePeerConnection()?.getLocalSSRC(track) : track.getSSRC();
+};
 
 /**
  * Handles track attached to container (Calls associateStreamWithVideoTag method
             : this.jvbJingleSession && this.jvbJingleSession.peerconnection;
 
     if (isLocal) {
-        // Local tracks have SSRC stored on per peer connection basis
+        // Local tracks have SSRC stored on per peer connection basis.
         if (peerConnection) {
             ssrc = peerConnection.getLocalSSRC(track);
         }

package-lock.json

         "@babel/plugin-syntax-optional-catch-binding": "^7.0.0"
       }
     },
+    "@babel/plugin-proposal-optional-chaining": {
+      "version": "7.2.0",
+      "resolved": "https://registry.npmjs.org/@babel/plugin-proposal-optional-chaining/-/plugin-proposal-optional-chaining-7.2.0.tgz",
+      "integrity": "sha512-ea3Q6edZC/55wEBVZAEz42v528VulyO0eir+7uky/sT4XRcdkWJcFi1aPtitTlwUzGnECWJNExWww1SStt+yWw==",
+      "dev": true,
+      "requires": {
+        "@babel/helper-plugin-utils": "^7.0.0",
+        "@babel/plugin-syntax-optional-chaining": "^7.2.0"
+      }
+    },
     "@babel/plugin-proposal-unicode-property-regex": {
       "version": "7.0.0",
       "resolved": "https://registry.npmjs.org/@babel/plugin-proposal-unicode-property-regex/-/plugin-proposal-unicode-property-regex-7.0.0.tgz",
         "@babel/helper-plugin-utils": "^7.0.0"
       }
     },
+    "@babel/plugin-syntax-optional-chaining": {
+      "version": "7.8.3",
+      "resolved": "https://registry.npmjs.org/@babel/plugin-syntax-optional-chaining/-/plugin-syntax-optional-chaining-7.8.3.tgz",
+      "integrity": "sha512-KoK9ErH1MBlCPxV0VANkXW2/dw4vlbGDrFgz8bmUsBGYkFRcbRwMh6cIJubdPrkxRwuGdtCk0v/wPTKbQgBjkg==",
+      "dev": true,
+      "requires": {
+        "@babel/helper-plugin-utils": "^7.8.0"
+      },
+      "dependencies": {
+        "@babel/helper-plugin-utils": {
+          "version": "7.10.4",
+          "resolved": "https://registry.npmjs.org/@babel/helper-plugin-utils/-/helper-plugin-utils-7.10.4.tgz",
+          "integrity": "sha512-O4KCvQA6lLiMU9l2eawBPMf1xPP8xPfB3iEQw150hOVTqj/rfXz0ThTb4HEzqQfs2Bmo5Ay8BzxfzVtBrr9dVg==",
+          "dev": true
+        }
+      }
+    },
     "@babel/plugin-transform-arrow-functions": {
       "version": "7.0.0",
       "resolved": "https://registry.npmjs.org/@babel/plugin-transform-arrow-functions/-/plugin-transform-arrow-functions-7.0.0.tgz",

package.json

     "@babel/core": "7.5.5",
     "@babel/plugin-proposal-class-properties": "7.1.0",
     "@babel/plugin-proposal-export-namespace-from": "7.0.0",
+    "@babel/plugin-proposal-optional-chaining": "7.2.0",
     "@babel/plugin-transform-flow-strip-types": "7.0.0",
     "@babel/preset-env": "7.1.0",
     "@babel/preset-flow": "7.0.0",

webpack-shared-config.js

                 plugins: [
                     '@babel/plugin-transform-flow-strip-types',
                     '@babel/plugin-proposal-class-properties',
+                    '@babel/plugin-proposal-optional-chaining',
                     '@babel/plugin-proposal-export-namespace-from'
                 ]
             },