feat: Expose unified VisionCameraProxy object, make FrameProcessorPlugins object-oriented (#1660)

* feat: Replace `FrameProcessorRuntimeManager` with `VisionCameraProxy` (iOS)

* Make `FrameProcessorPlugin` a constructable HostObject

* fix: Fix `name` override

* Simplify `useFrameProcessor

* fix: Fix lint errors

* Remove FrameProcessorPlugin::name

* JSIUtils -> JSINSObjectConversion

example/ios/Frame Processor Plugins/Example Plugin/ExampleFrameProcessorPlugin.m

@@ -0,0 +1,49 @@
+//
+//  ExampleFrameProcessorPlugin.m
+//  VisionCameraExample
+//
+//  Created by Marc Rousavy on 01.05.21.
+//
+
+#if __has_include(<VisionCamera/FrameProcessorPlugin.h>)
+#import <Foundation/Foundation.h>
+#import <VisionCamera/FrameProcessorPlugin.h>
+#import <VisionCamera/FrameProcessorPluginRegistry.h>
+#import <VisionCamera/Frame.h>
+
+// Example for an Objective-C Frame Processor plugin
+
+@interface ExampleFrameProcessorPlugin : FrameProcessorPlugin
+@end
+
+@implementation ExampleFrameProcessorPlugin
+
+- (id)callback:(Frame *)frame withArguments:(NSArray<id> *)arguments {
+  CVPixelBufferRef imageBuffer = CMSampleBufferGetImageBuffer(frame.buffer);
+  NSLog(@"ExamplePlugin: %zu x %zu Image. Logging %lu parameters:", CVPixelBufferGetWidth(imageBuffer), CVPixelBufferGetHeight(imageBuffer), (unsigned long)arguments.count);
+
+  for (id param in arguments) {
+    NSLog(@"ExamplePlugin:   -> %@ (%@)", param == nil ? @"(nil)" : [param description], NSStringFromClass([param classForCoder]));
+  }
+
+  return @{
+    @"example_str": @"Test",
+    @"example_bool": @true,
+    @"example_double": @5.3,
+    @"example_array": @[
+      @"Hello",
+      @true,
+      @17.38
+    ]
+  };
+}
+
++ (void) load {
+  [FrameProcessorPluginRegistry addFrameProcessorPlugin:@"example_plugin"
+                                        withInitializer:^FrameProcessorPlugin*(NSDictionary* options) {
+    return [[ExampleFrameProcessorPlugin alloc] initWithOptions:options];
+  }];
+}
+
+@end
+#endif