docs: Add Kotlin & Swift FP plugins examples (#1902)

* chore(docs): add Kotlin FP example

* chore(docs): add Swift FP plugin

package/example/ios/Frame Processor Plugins/Example Swift Plugin/ExampleSwiftFrameProcessor.m

@@ -0,0 +1,31 @@
+//
+//  ExampleSwiftFrameProcessor.m
+//  VisionCameraExample
+//
+//  Created by Mateusz Medrek on 02/10/2023.
+//
+
+#if __has_include(<VisionCamera/FrameProcessorPlugin.h>)
+#import <Foundation/Foundation.h>
+#import <VisionCamera/FrameProcessorPlugin.h>
+#import <VisionCamera/FrameProcessorPluginRegistry.h>
+#import <VisionCamera/Frame.h>
+
+#import "VisionCameraExample-Swift.h"
+
+// Example for a Swift Frame Processor plugin automatic registration
+@interface ExampleSwiftFrameProcessorPlugin (FrameProcessorPluginLoader)
+@end
+
+@implementation ExampleSwiftFrameProcessorPlugin (FrameProcessorPluginLoader)
+
++ (void)load
+{
+  [FrameProcessorPluginRegistry addFrameProcessorPlugin:@"example_kotlin_swift_plugin" withInitializer:^FrameProcessorPlugin * _Nonnull(NSDictionary * _Nullable options) {
+    return [[ExampleSwiftFrameProcessorPlugin alloc] init];
+  }];
+}
+
+@end
+
+#endif

package/example/ios/Frame Processor Plugins/Example Swift Plugin/ExampleSwiftFrameProcessor.swift

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+//
+//  ExampleSwiftFrameProcessor.swift
+//  VisionCameraExample
+//
+//  Created by Mateusz Medrek on 02/10/2023.
+//
+
+#if VISION_CAMERA_ENABLE_FRAME_PROCESSORS
+import VisionCamera
+
+// Example for a Swift Frame Processor plugin
+@objc(ExampleSwiftFrameProcessorPlugin)
+public class ExampleSwiftFrameProcessorPlugin: FrameProcessorPlugin {
+  public override func callback(_ frame: Frame, withArguments arguments: [AnyHashable: Any]?) -> Any? {
+    let imageBuffer = CMSampleBufferGetImageBuffer(frame.buffer)
+
+    if let arguments, let imageBuffer {
+      let width = CVPixelBufferGetWidth(imageBuffer)
+      let height = CVPixelBufferGetHeight(imageBuffer)
+      let count = arguments.count
+
+      print(
+        "ExampleSwiftPlugin: \(width) x \(height) Image. Logging \(count) parameters:"
+      )
+
+      for key in arguments.keys {
+        let value = arguments[key]
+        let valueString = String(describing: value)
+        let valueClassString = String(describing: value.self)
+        print("ExampleSwiftPlugin:   -> \(valueString) (\(valueClassString))")
+      }
+    }
+
+    return [
+      "example_str": "SwiftTest",
+      "example_bool": false,
+      "example_double": 6.7,
+      "example_array": ["Good bye", false, 21.37]
+    ]
+  }
+}
+#endif