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/Video/RCTVideoManager.swift

@@ -0,0 +1,63 @@
+import AVFoundation
+import React
+
+@objc(RCTVideoManager)
+class RCTVideoManager: RCTViewManager {
+    
+    override func view() -> UIView {
+        return RCTVideo(eventDispatcher: bridge.eventDispatcher())
+    }
+    
+    func methodQueue() -> DispatchQueue {
+        return bridge.uiManager.methodQueue
+    }
+    
+    @objc(save:reactTag:resolver:rejecter:)
+    func save(options: NSDictionary, reactTag: NSNumber, resolve: @escaping RCTPromiseResolveBlock,reject: @escaping RCTPromiseRejectBlock) -> Void {
+        bridge.uiManager.prependUIBlock({_ , viewRegistry in
+            let view = viewRegistry?[reactTag]
+            if !(view is RCTVideo) {
+                RCTLogError("Invalid view returned from registry, expecting RCTVideo, got: %@", String(describing: view))
+            } else if let view = view as? RCTVideo {
+                view.save(options: options, resolve: resolve, reject: reject)
+            }
+        })
+    }
+    
+    @objc(setLicenseResult:reactTag:)
+    func setLicenseResult(license: NSString, reactTag: NSNumber) -> Void {
+        bridge.uiManager.prependUIBlock({_ , viewRegistry in
+            let view = viewRegistry?[reactTag]
+            if !(view is RCTVideo) {
+                RCTLogError("Invalid view returned from registry, expecting RCTVideo, got: %@", String(describing: view))
+            } else if let view = view as? RCTVideo {
+                view.setLicenseResult(license as String)
+            }
+        })
+    }
+    
+    @objc(setLicenseResultError:reactTag:)
+    func setLicenseResultError(error: NSString, reactTag: NSNumber) -> Void {
+        bridge.uiManager.prependUIBlock({_ , viewRegistry in
+            let view = viewRegistry?[reactTag]
+            if !(view is RCTVideo) {
+                RCTLogError("Invalid view returned from registry, expecting RCTVideo, got: %@", String(describing: view))
+            } else if let view = view as? RCTVideo {
+                view.setLicenseResultError(error as String)
+            }
+        })
+    }
+    
+    override func constantsToExport() -> [AnyHashable : Any]? {
+        return [
+            "ScaleNone": AVLayerVideoGravity.resizeAspect,
+            "ScaleToFill": AVLayerVideoGravity.resize,
+            "ScaleAspectFit": AVLayerVideoGravity.resizeAspect,
+            "ScaleAspectFill": AVLayerVideoGravity.resizeAspectFill
+        ]
+    }
+
+    override class func requiresMainQueueSetup() -> Bool {
+        return true
+    }
+}