fix(FEC-12539): Shaka text displayer font size too small on TVs (#208)

solves: FEC-12539 - Regression 

**issue:** the previous fix is incorrect since the media query refers to the screen size and not the player size

**fix:** The :fullscreen [CSS](https://developer.mozilla.org/en-US/docs/Web/CSS) [pseudo-class](https://developer.mozilla.org/en-US/docs/Web/CSS/Pseudo-classes) is not applied in samrtTvs, so instead i relying on the Env.IsSmartTv env variable

src/assets/style.css

@@ -35,9 +35,3 @@
 :-ms-fullscreen .shaka-text-container {
   font-size: 4.4vmin;
 }
-
-@media screen and (min-width: 1240px) {
-  .shaka-text-container {
-    font-size: 4.4vmin;
-  }
-}

src/dash-adapter.js

@@ -1,6 +1,7 @@
 // @flow
 import shaka from 'shaka-player';
 import {
+  Env,
   AudioTrack,
   BaseMediaSourceAdapter,
   Error,
@@ -398,17 +399,24 @@ export default class DashAdapter extends BaseMediaSourceAdapter {
     //Need to call this again cause we are uninstalling the VTTCue polyfill to avoid collisions with other libs
     shaka.polyfill.installAll();
     this._shaka = new shaka.Player();
-    // This will force the player to use shaka UITextDisplayer plugin to render text tracks.
-    if (this._config.useShakaTextTrackDisplay) {
-      this._shaka.setVideoContainer(Utils.Dom.getElementBySelector('.playkit-subtitles'));
-    }
+    this._setTextDisplayer();
     this._maybeSetFilters();
     this._maybeSetDrmConfig();
     this._maybeBreakStalls();
     this._shaka.configure(this._config.shakaConfig);
     this._addBindings();
   }
 
+  _setTextDisplayer() {
+    // This will force the player to use shaka UITextDisplayer plugin to render text tracks.
+    if (this._config.useShakaTextTrackDisplay) {
+      this._shaka.setVideoContainer(Utils.Dom.getElementBySelector('.playkit-subtitles'));
+      if (Env.isSmartTV) {
+        document.querySelector('.shaka-text-container').style.fontsize = '4.4vmin';
+      }
+    }
+  }
+
   _clearStallInterval(): void {
     if (this._stallInterval) {
       clearInterval(this._stallInterval);