iOS Swift Conversion (#2527)

Converts iOS implementation from Objective-c to Swift

# During the conversion process some updates to the code structure were also made
- Modularize codebase from single file to smaller focused files
- Untangled large nested IF statements
- Added more null checks, since Swift is more strict with null pointers
- Added property to allow for decoding of local video sources with self contained key for offline playback
- Updates example apps to test react-native 0.63.4 and uses auto native dependency imports for android and ios

ios/VideoCaching/RCTVideoCachingHandler.swift

@@ -0,0 +1,87 @@
+import Foundation
+import AVFoundation
+import DVAssetLoaderDelegate
+import Promises
+
+class RCTVideoCachingHandler: NSObject, DVAssetLoaderDelegatesDelegate {
+    
+    private var _videoCache:RCTVideoCache! = RCTVideoCache.sharedInstance()
+    var playerItemPrepareText: ((AVAsset?, NSDictionary?) -> AVPlayerItem)?
+    
+    override init() {
+        super.init()
+    }
+    
+    func shouldCache(source: VideoSource, textTracks:[TextTrack]?) -> Bool {
+        if source.isNetwork && source.shouldCache && ((textTracks == nil) || (textTracks!.count == 0)) {
+            /* The DVURLAsset created by cache doesn't have a tracksWithMediaType property, so trying
+             * to bring in the text track code will crash. I suspect this is because the asset hasn't fully loaded.
+             * Until this is fixed, we need to bypass caching when text tracks are specified.
+             */
+            DebugLog("Caching is not supported for uri '\(source.uri)' because text tracks are not compatible with the cache. Checkout https://github.com/react-native-community/react-native-video/blob/master/docs/caching.md")
+            return true
+        }
+        return false
+    }
+    
+    func playerItemForSourceUsingCache(uri:String!, assetOptions options:NSDictionary!) -> Promise<AVPlayerItem?> {
+        let url = URL(string: uri)
+        return getItemForUri(uri)
+        .then{ [weak self] (videoCacheStatus:RCTVideoCacheStatus,cachedAsset:AVAsset?) -> AVPlayerItem in
+            guard let self = self, let playerItemPrepareText = self.playerItemPrepareText else {throw  NSError(domain: "", code: 0, userInfo: nil)}
+            switch (videoCacheStatus) {
+            case .missingFileExtension:
+                DebugLog("Could not generate cache key for uri '\(uri)'. It is currently not supported to cache urls that do not include a file extension. The video file will not be cached. Checkout https://github.com/react-native-community/react-native-video/blob/master/docs/caching.md")
+                let asset:AVURLAsset! = AVURLAsset(url: url!, options:options as! [String : Any])
+                return playerItemPrepareText(asset, options)
+                
+            case .unsupportedFileExtension:
+                DebugLog("Could not generate cache key for uri '\(uri)'. The file extension of that uri is currently not supported. The video file will not be cached. Checkout https://github.com/react-native-community/react-native-video/blob/master/docs/caching.md")
+                let asset:AVURLAsset! = AVURLAsset(url: url!, options:options as! [String : Any])
+                return playerItemPrepareText(asset, options)
+                
+            default:
+                if let cachedAsset = cachedAsset {
+                    DebugLog("Playing back uri '\(uri)' from cache")
+                    // See note in playerItemForSource about not being able to support text tracks & caching
+                    return AVPlayerItem(asset: cachedAsset)
+                }
+            }
+            
+            let asset:DVURLAsset! = DVURLAsset(url:url, options:options as! [String : Any], networkTimeout:10000)
+            asset.loaderDelegate = self
+            
+            /* More granular code to have control over the DVURLAsset
+             let resourceLoaderDelegate = DVAssetLoaderDelegate(url: url)
+             resourceLoaderDelegate.delegate = self
+             let components = NSURLComponents(url: url, resolvingAgainstBaseURL: false)
+             components?.scheme = DVAssetLoaderDelegate.scheme()
+             var asset: AVURLAsset? = nil
+             if let url = components?.url {
+             asset = AVURLAsset(url: url, options: options)
+             }
+             asset?.resourceLoader.setDelegate(resourceLoaderDelegate, queue: DispatchQueue.main)
+             */
+            
+            return AVPlayerItem(asset: asset)
+        }
+    }
+
+    func getItemForUri(_ uri:String) ->  Promise<(videoCacheStatus:RCTVideoCacheStatus,cachedAsset:AVAsset?)> {
+        return Promise<(videoCacheStatus:RCTVideoCacheStatus,cachedAsset:AVAsset?)> { fulfill, reject in
+            self._videoCache.getItemForUri(uri, withCallback:{ (videoCacheStatus:RCTVideoCacheStatus,cachedAsset:AVAsset?) in
+                fulfill((videoCacheStatus, cachedAsset))
+            })
+        }
+    }
+    
+    // MARK: - DVAssetLoaderDelegate
+    
+    func dvAssetLoaderDelegate(loaderDelegate:DVAssetLoaderDelegate!, didLoadData data:NSData!, forURL url:NSURL!) {
+        _videoCache.storeItem(data as Data?, forUri:url.absoluteString, withCallback:{ (success:Bool) in
+            DebugLog("Cache data stored successfully 🎉")
+        })
+    }
+    
+}
+