feat: implement opacity to control visibility of subtitles (#3583)

* feat: implement opacity to control visibility of subtitles

implemented per discussion on https://github.com/react-native-video/react-native-video/issues/3579

updated docs and linked onTextTrackDataChanged to the subtitle style to clarify intent on how to control visibility.

* chore: update type so that we use a union of 0 1 vs any number

* chore: run ktlint to get rid of white spaces

* feat: add ability to have range of numbers for opacity; while, 0 will still not render the subtitles.

added util function for safeGetFloat

updated types

* feat: add ability to suppress subtitles with opacity 0

add data structure for subtitle styles for extensibility

* chore: run yarn check-ios

* chore: update documentation to clarify differences between android and ios

* Update android/src/main/java/com/brentvatne/exoplayer/ExoPlayerView.java

Co-authored-by: Olivier Bouillet <62574056+freeboub@users.noreply.github.com>

---------

Co-authored-by: Olivier Bouillet <62574056+freeboub@users.noreply.github.com>

src/specs/VideoNativeComponent.ts

@@ -118,6 +118,7 @@ type SubtitleStyle = Readonly<{
   paddingBottom?: WithDefault<Float, 0>;
   paddingLeft?: WithDefault<Float, 0>;
   paddingRight?: WithDefault<Float, 0>;
+  opacity?: WithDefault<Float, 1>;
 }>;
 
 export type OnLoadData = Readonly<{

src/types/video.ts

@@ -104,6 +104,7 @@ export type SubtitleStyle = {
   paddingBottom?: number;
   paddingLeft?: number;
   paddingRight?: number;
+  opacity?: number;
 };
 
 export enum TextTracksType {