fix(WebVTT): Fix wrong writing-mode in nested cues (#5807)

Fixes #4765

Backported to v4.3.x

lib/text/vtt_text_parser.js

@@ -403,8 +403,6 @@ shaka.text.VttTextParser = class {
       cue = new shaka.text.Cue(start, end, '');
     }
 
-    VttTextParser.parseCueStyles(payload, cue, styles);
-
     // Parse optional settings.
     parser.skipWhitespace();
     let word = parser.readWord();
@@ -418,6 +416,8 @@ shaka.text.VttTextParser = class {
       word = parser.readWord();
     }
 
+    VttTextParser.parseCueStyles(payload, cue, styles);
+
     if (id != null) {
       cue.id = id;
     }
@@ -688,6 +688,14 @@ shaka.text.VttTextParser = class {
   static generateCueFromElement_(element, rootCue, cues, styles) {
     const VttTextParser = shaka.text.VttTextParser;
     const nestedCue = rootCue.clone();
+    // We don't want propagate some properties.
+    nestedCue.nestedCues = [];
+    nestedCue.payload = '';
+    // We don't want propagate some position settings
+    nestedCue.line = null;
+    nestedCue.region = new shaka.text.CueRegion();
+    nestedCue.position = null;
+    nestedCue.size = 0;
     if (element.nodeType === Node.ELEMENT_NODE && element.nodeName) {
       const bold = shaka.text.Cue.fontWeight.BOLD;
       const italic = shaka.text.Cue.fontStyle.ITALIC;