[cscore] Add support for USB cameras on macOS (#4846)

The main restriction is there must be an event loop running on the main thread.
No special action is required for GUI applications, but for non-GUI applications, a
RunOsxRunLoop() function is provided that needs to be called from the main thread.

cscore/src/main/native/objcpp/UsbCameraImplObjc.h

@@ -0,0 +1,71 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#import <AVFoundation/AVFoundation.h>
+#import "UsbCameraDelegate.h"
+#include <memory>
+#include <string_view>
+#include "cscore_cpp.h"
+
+namespace cs {
+class UsbCameraImpl;
+}
+
+@interface UsbCameraImplObjc : NSObject
+
+@property(nonatomic) AVCaptureDeviceFormat* currentFormat;
+@property(nonatomic) int currentFPS;
+@property(nonatomic) std::weak_ptr<cs::UsbCameraImpl> cppImpl;
+@property(nonatomic) dispatch_queue_t sessionQueue;
+@property(nonatomic) NSString* path;
+@property(nonatomic) int deviceId;
+@property(nonatomic) bool propertiesCached;
+@property(nonatomic) bool streaming;
+@property(nonatomic) bool deviceValid;
+@property(nonatomic) bool isAuthorized;
+
+@property(nonatomic) AVCaptureDevice* videoDevice;
+@property(nonatomic) AVCaptureDeviceInput* videoInput;
+@property(nonatomic) UsbCameraDelegate* callback;
+@property(nonatomic) AVCaptureVideoDataOutput* videoOutput;
+@property(nonatomic) AVCaptureSession* session;
+
+- (void)start;
+
+// Property functions
+- (void)setProperty:(int)property
+          withValue:(int)value
+             status:(CS_Status*)status;
+- (void)setStringProperty:(int)property
+                withValue:(std::string_view*)value
+                   status:(CS_Status*)status;
+
+// Standard common camera properties
+- (void)setBrightness:(int)brightness status:(CS_Status*)status;
+- (int)getBrightness:(CS_Status*)status;
+- (void)setWhiteBalanceAuto:(CS_Status*)status;
+- (void)setWhiteBalanceHoldCurrent:(CS_Status*)status;
+- (void)setWhiteBalanceManual:(int)value status:(CS_Status*)status;
+- (void)setExposureAuto:(CS_Status*)status;
+- (void)setExposureHoldCurrent:(CS_Status*)status;
+- (void)setExposureManual:(int)value status:(CS_Status*)status;
+
+- (bool)setVideoMode:(const cs::VideoMode&)mode status:(CS_Status*)status;
+- (bool)setPixelFormat:(cs::VideoMode::PixelFormat)pixelFormat
+                status:(CS_Status*)status;
+- (bool)setResolutionWidth:(int)width
+                withHeight:(int)height
+                    status:(CS_Status*)status;
+- (bool)setFPS:(int)fps status:(CS_Status*)status;
+
+- (void)numSinksChanged;
+- (void)numSinksEnabledChanged;
+
+- (void)getCurrentCameraPath:(std::string*)path;
+- (void)getCameraName:(std::string*)name;
+- (void)setNewCameraPath:(std::string_view*)path;
+
+@end