fix: Prefer SimpleTextDisplayer on iOS (#7569)

Fixes #7568

lib/player.js

@@ -6513,7 +6513,12 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
     // Because this.video_ may not be set when the config is built, the default
     // TextDisplay factory must capture a reference to "this".
     config.textDisplayFactory = () => {
-      if (this.videoContainer_) {
+      // On iOS where the Fullscreen API is not available we prefer
+      // SimpleTextDisplayer because it works with the Fullscreen API of the
+      // video element itself.
+      const Platform = shaka.util.Platform;
+      if (this.videoContainer_ &&
+          (!Platform.safariVersion() || document.fullscreenEnabled)) {
         const latestConfig = this.getConfiguration();
         return new shaka.text.UITextDisplayer(
             this.video_, this.videoContainer_, latestConfig.textDisplayer);

lib/text/ui_text_displayer.js

@@ -9,6 +9,7 @@ goog.provide('shaka.text.UITextDisplayer');
 
 goog.require('goog.asserts');
 goog.require('shaka.Deprecate');
+goog.require('shaka.log');
 goog.require('shaka.text.Cue');
 goog.require('shaka.text.CueRegion');
 goog.require('shaka.text.Utils');
@@ -35,6 +36,12 @@ shaka.text.UITextDisplayer = class {
   constructor(video, videoContainer, config) {
     goog.asserts.assert(videoContainer, 'videoContainer should be valid.');
 
+    if (!document.fullscreenEnabled) {
+      shaka.log.alwaysWarn('Using UITextDisplayer in a browser without ' +
+          'Fullscreen API support causes subtitles to not be rendered in ' +
+          'fullscreen');
+    }
+
     /** @private {boolean} */
     this.isTextVisible_ = false;