VEX-3245: Buffer Progress UI While Paused (#7)

Add support for onBufferProgress prop on Android to get buffer data even when the player is paused.

README.md

@@ -321,6 +321,7 @@ var styles = StyleSheet.create({
 ### Event props
 * [onAudioBecomingNoisy](#onaudiobecomingnoisy)
 * [onBandwidthUpdate](#onbandwidthupdate)
+* [onBufferProgress](#onbufferprogress)
 * [onEnd](#onend)
 * [onExternalPlaybackChange](#onexternalplaybackchange)
 * [onFullscreenPlayerWillPresent](#onfullscreenplayerwillpresent)
@@ -944,6 +945,18 @@ Note: On Android ExoPlayer, you must set the [reportBandwidth](#reportbandwidth)
 
 Platforms: Android ExoPlayer
 
+
+#### onBufferProgress
+Callback function that is called on a set interval which contains the buffer start and end position in ms.
+
+Payload:
+Property | Type | Description
+--- | --- | ---
+start | number | The buffer start (ms)
+end | number | The buffer end (ms)
+
+Platforms: Android ExoPlayer
+
 #### onEnd
 Callback function that is called when the player reaches the end of the media.