ref: move all prop type declaration to flow

For the most part the changes are taking the "static propTypes" declaration off
of components and declaring them as Flow types. Sometimes to support flow some
method signatures had to be added. There are some exceptions in which more had
to be done to tame the beast:
- AbstractVideoTrack: put in additional truthy checks for videoTrack.
- Video: add truthy checks for the _videoElement ref.
- shouldRenderVideoTrack function: Some component could pass null for the
  videoTrack argument and Flow wanted that called out explicitly.
- DisplayName: Add a truthy check for the input ref before acting on it.
- NumbersList: Move array checks inline for Flow to comprehend array methods
  could be called. Add type checks in the Object.entries loop as the value is
  assumed to be a mixed type by Flow.
- AbstractToolbarButton: add additional truthy check for passed in type.

react/features/invite/components/AddPeopleDialog.web.js

@@ -2,7 +2,6 @@
 
 import Avatar from '@atlaskit/avatar';
 import InlineMessage from '@atlaskit/inline-message';
-import PropTypes from 'prop-types';
 import React, { Component } from 'react';
 import { connect } from 'react-redux';
 
@@ -19,88 +18,96 @@ const logger = require('jitsi-meet-logger').getLogger(__filename);
 
 declare var interfaceConfig: Object;
 
+/**
+ * The type of the React {@code Component} props of {@link AddPeopleDialog}.
+ */
+type Props = {
+
+    /**
+     * The {@link JitsiMeetConference} which will be used to invite "room"
+     * participants through the SIP Jibri (Video SIP gateway).
+     */
+    _conference: Object,
+
+    /**
+     * The URL for validating if a phone number can be called.
+     */
+    _dialOutAuthUrl: string,
+
+    /**
+     * Whether to show a footer text after the search results as a last element.
+     */
+    _footerTextEnabled: boolean,
+
+    /**
+     * The JWT token.
+     */
+    _jwt: string,
+
+    /**
+     * The query types used when searching people.
+     */
+    _peopleSearchQueryTypes: Array<string>,
+
+    /**
+     * The URL pointing to the service allowing for people search.
+     */
+    _peopleSearchUrl: string,
+
+    /**
+     * Whether or not to show Add People functionality.
+     */
+    addPeopleEnabled: boolean,
+
+    /**
+     * Whether or not to show Dial Out functionality.
+     */
+    dialOutEnabled: boolean,
+
+    /**
+     * The redux {@code dispatch} function.
+     */
+    dispatch: Dispatch<*>,
+
+    /**
+     * Invoked to obtain translated strings.
+     */
+    t: Function,
+};
+
+/**
+ * The type of the React {@code Component} state of {@link AddPeopleDialog}.
+ */
+type State = {
+
+    /**
+     * Indicating that an error occurred when adding people to the call.
+     */
+    addToCallError: boolean,
+
+    /**
+     * Indicating that we're currently adding the new people to the
+     * call.
+     */
+    addToCallInProgress: boolean,
+
+    /**
+     * The list of invite items.
+     */
+    inviteItems: Array<Object>
+};
+
 /**
  * The dialog that allows to invite people to the call.
  */
-class AddPeopleDialog extends Component<*, *> {
-    /**
-     * {@code AddPeopleDialog}'s property types.
-     *
-     * @static
-     */
-    static propTypes = {
-        /**
-         * The {@link JitsiMeetConference} which will be used to invite "room"
-         * participants through the SIP Jibri (Video SIP gateway).
-         */
-        _conference: PropTypes.object,
-
-        /**
-         * The URL for validating if a phone number can be called.
-         */
-        _dialOutAuthUrl: PropTypes.string,
-
-        /**
-         * Whether to show a footer text after the search results
-         * as a last element.
-         */
-        _footerTextEnabled: PropTypes.bool,
-
-        /**
-         * The JWT token.
-         */
-        _jwt: PropTypes.string,
-
-        /**
-         * The query types used when searching people.
-         */
-        _peopleSearchQueryTypes: PropTypes.arrayOf(PropTypes.string),
-
-        /**
-         * The URL pointing to the service allowing for people search.
-         */
-        _peopleSearchUrl: PropTypes.string,
-
-        /**
-         * Whether or not to show Add People functionality.
-         */
-        addPeopleEnabled: PropTypes.bool,
-
-        /**
-         * Whether or not to show Dial Out functionality.
-         */
-        dialOutEnabled: PropTypes.bool,
-
-        /**
-         * The redux {@code dispatch} function.
-         */
-        dispatch: PropTypes.func,
-
-        /**
-         * Invoked to obtain translated strings.
-         */
-        t: PropTypes.func
-    };
-
+class AddPeopleDialog extends Component<Props, State> {
     _multiselect = null;
 
     _resourceClient: Object;
 
     state = {
-        /**
-         * Indicating that an error occurred when adding people to the call.
-         */
         addToCallError: false,
-
-        /**
-         * Indicating that we're currently adding the new people to the
-         * call.
-         */
         addToCallInProgress: false,
-
-        /**
-         * The list of invite items.
-         */
         inviteItems: []
     };
 
@@ -110,7 +117,7 @@ class AddPeopleDialog extends Component<*, *> {
      * @param {Object} props - The read-only properties with which the new
      * instance is to be initialized.
      */
-    constructor(props) {
+    constructor(props: Props) {
         super(props);
 
         // Bind event handlers so they are only bound once per instance.
@@ -142,10 +149,11 @@ class AddPeopleDialog extends Component<*, *> {
     /**
      * React Component method that executes once component is updated.
      *
+     * @param {Object} prevProps - The state object before the update.
      * @param {Object} prevState - The state object before the update.
      * @returns {void}
      */
-    componentDidUpdate(prevState) {
+    componentDidUpdate(prevProps, prevState) {
         /**
          * Clears selected items from the multi select component on successful
          * invite.