fix(chat): polyfills for lib-jitsi-meet ChatRoom#onPresence (#2678)

The onPresence parsing was refactored to remove use of jQuery.
This exposed three methods not available in react-native:
ParentNode.children, ChildNode.remove, and
document.querySelectorAll. The querySelectorAll change could
be swapped for the already polyfilled querySelector, but
children and remove had to be added. The polyfills are based
on those supplied by MDN web docs, but modified to pass jitsi
linting.

react/features/base/lib-jitsi-meet/native/polyfills-browser.js

@@ -195,6 +195,18 @@ function _visitNode(node, callback) {
                 };
             }
 
+            // Element.remove
+            //
+            // Required by:
+            // - lib-jitsi-meet ChatRoom#onPresence parsing
+            if (typeof elementPrototype.remove === 'undefined') {
+                elementPrototype.remove = function() {
+                    if (this.parentNode !== null) {
+                        this.parentNode.removeChild(this);
+                    }
+                };
+            }
+
             // Element.innerHTML
             //
             // Required by:
@@ -231,6 +243,31 @@ function _visitNode(node, callback) {
                     }
                 });
             }
+
+            // Element.children
+            //
+            // Required by:
+            // - lib-jitsi-meet ChatRoom#onPresence parsing
+            if (!elementPrototype.hasOwnProperty('children')) {
+                Object.defineProperty(elementPrototype, 'children', {
+                    get() {
+                        const nodes = this.childNodes;
+                        const children = [];
+                        let i = 0;
+                        let node = nodes[i];
+
+                        while (node) {
+                            if (node.nodeType === 1) {
+                                children.push(node);
+                            }
+                            i += 1;
+                            node = nodes[i];
+                        }
+
+                        return children;
+                    }
+                });
+            }
         }
 
         // FIXME There is a weird infinite loop related to console.log and