feat: New Core/ library (#1975)

Moves everything Camera related into `core/` / `Core/` so that it is better encapsulated from React Native.

Benefits:

1. Code is much better organized. Should be easier for collaborators now, and cleaner codebase for me.
2. Locking is fully atomically as you can now only configure the session through a lock/Mutex which is batch-overridable
    * On iOS, this makes Camera startup time **MUCH** faster, I measured speedups from **1.5 seconds** to only **240 milliseconds** since we only lock/commit once! 🚀 
    * On Android, this fixes a few out-of-sync/concurrency issues like "Capture Request contains unconfigured Input/Output Surface!" since it is now a single lock-operation! 💪 
3. It is easier to integrate VisionCamera outside of React Native (e.g. Native iOS Apps, NativeScript, Flutter, etc)

With this PR, VisionCamera V3 is up to **7x** faster than V2

package/ios/Core/PreviewView.swift

@@ -0,0 +1,59 @@
+//
+//  PreviewView.swift
+//  VisionCamera
+//
+//  Created by Marc Rousavy on 30.11.22.
+//  Copyright © 2022 mrousavy. All rights reserved.
+//
+
+import AVFoundation
+import Foundation
+import UIKit
+
+class PreviewView: UIView {
+  /**
+   Convenience wrapper to get layer as its statically known type.
+   */
+  var videoPreviewLayer: AVCaptureVideoPreviewLayer {
+    // swiftlint:disable force_cast
+    return layer as! AVCaptureVideoPreviewLayer
+    // swiftlint:enable force_cast
+  }
+
+  /**
+   Gets or sets the resize mode of the PreviewView.
+   */
+  var resizeMode: ResizeMode = .cover {
+    didSet {
+      switch resizeMode {
+      case .cover:
+        videoPreviewLayer.videoGravity = .resizeAspectFill
+      case .contain:
+        videoPreviewLayer.videoGravity = .resizeAspect
+      }
+    }
+  }
+
+  override public class var layerClass: AnyClass {
+    return AVCaptureVideoPreviewLayer.self
+  }
+
+  func layerRectConverted(fromMetadataOutputRect rect: CGRect) -> CGRect {
+    return videoPreviewLayer.layerRectConverted(fromMetadataOutputRect: rect)
+  }
+
+  func captureDevicePointConverted(fromLayerPoint point: CGPoint) -> CGPoint {
+    return videoPreviewLayer.captureDevicePointConverted(fromLayerPoint: point)
+  }
+
+  init(frame: CGRect, session: AVCaptureSession) {
+    super.init(frame: frame)
+    videoPreviewLayer.session = session
+    videoPreviewLayer.videoGravity = .resizeAspectFill
+  }
+
+  @available(*, unavailable)
+  required init?(coder _: NSCoder) {
+    fatalError("init(coder:) is not implemented!")
+  }
+}