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

react-native-video.podspec

@@ -12,12 +12,12 @@ Pod::Spec.new do |s|
   s.homepage       = 'https://github.com/react-native-video/react-native-video'
   s.source       = { :git => "https://github.com/react-native-video/react-native-video.git", :tag => "v#{s.version}" }
 
-  s.ios.deployment_target = "8.0"
+  s.ios.deployment_target = "9.0"
   s.tvos.deployment_target = "9.0"
 
   s.subspec "Video" do |ss|
-    ss.source_files  = "ios/Video/*.{h,m}"
-    s.static_framework = true
+    ss.source_files  = "ios/Video/**/*.{h,m,swift}"
+    ss.dependency "PromisesSwift"
   end
 
   s.subspec "VideoCaching" do |ss|
@@ -25,14 +25,15 @@ Pod::Spec.new do |s|
     ss.dependency "SPTPersistentCache", "~> 1.1.0"
     ss.dependency "DVAssetLoaderDelegate", "~> 0.3.1"
 
-    ss.source_files = "ios/VideoCaching/**/*.{h,m}"
-    s.static_framework = true
+    ss.source_files = "ios/VideoCaching/**/*.{h,m,swift}"
   end
 
   s.dependency "React-Core"
 
   s.default_subspec = "Video"
 
+  s.static_framework = true
+
   s.xcconfig = {
     'OTHER_LDFLAGS': '-ObjC',
   }