Mute video when autoplay is blocked by browser policy (#6087)

## Issue
When opening a video directly in Chrome Incognito, the video should autoplay (since that's the default Lbry setting), but it doesn't due to browser policy
https://developers.google.com/web/updates/2017/09/autoplay-policy-changes

## Changes
- We don't want to forcefully mute the video when `autoplay=true`; we just want to do it when the browser policy is applied.
- Fortunately, there is already an existing code-block for us to check that.

## Test cases
- [x] "Autoplay=Off" should not be affected.
- [x] After manually unmuting, the next autoplayed video should not be muted (this is "user interacted" opening, so the policy allows autoplay)
- [x] If manually muting, the next autoplayed video should retain user's last setting.

## Known issues
- I've seen `error` occasionally being undefined in the `catch` block. In those cases, the solution doesn't work. We could remove `if (player.autoplay() && !player.muted())` and simply just try muting it, but for now it's better to ensure `NotAllowedError` is due to unmuted first before applying the fix.
- This doesn't work for Firefox as there is an explicit "Allow Autoplay" button in the address bar that user needs to click themselves. Applies to all sites.

ui/component/viewers/videoViewer/internal/videojs.jsx

@@ -38,6 +38,7 @@ export type Player = {
   controlBar: {
     addChild: (string, any) => void,
   },
+  autoplay: (any) => boolean,
 };
 
 type Props = {

ui/component/viewers/videoViewer/view.jsx

@@ -221,6 +221,12 @@ function VideoViewer(props: Props) {
       );
 
       Promise.race([playPromise, timeoutPromise]).catch((error) => {
+        if (typeof error === 'object' && error.name && error.name === 'NotAllowedError') {
+          if (player.autoplay() && !player.muted()) {
+            player.muted(true);
+          }
+        }
+
         if (PLAY_TIMEOUT_ERROR) {
           const retryPlayPromise = player.play();
           Promise.race([retryPlayPromise, timeoutPromise]).catch((error) => {