camera: Massive code reworking.

- Simplified public API, simplified backend interface.
- Camera device hotplug events.
- Thread code is split up so it backends that provide own threads can use it.
- Added "dummy" backend.

Note that CoreMedia (Apple) and Android backends need to be updated, as does
the testcamera app (testcameraminimal works).

src/dynapi/SDL_dynapi_overrides.h

@@ -982,19 +982,16 @@
 #define SDL_SetWindowShape SDL_SetWindowShape_REAL
 #define SDL_RenderViewportSet SDL_RenderViewportSet_REAL
 #define SDL_HasProperty SDL_HasProperty_REAL
+#define SDL_GetNumCameraDrivers SDL_GetNumCameraDrivers_REAL
+#define SDL_GetCameraDriver SDL_GetCameraDriver_REAL
+#define SDL_GetCurrentCameraDriver SDL_GetCurrentCameraDriver_REAL
 #define SDL_GetCameraDevices SDL_GetCameraDevices_REAL
-#define SDL_OpenCamera SDL_OpenCamera_REAL
-#define SDL_SetCameraSpec SDL_SetCameraSpec_REAL
-#define SDL_OpenCameraWithSpec SDL_OpenCameraWithSpec_REAL
+#define SDL_GetCameraDeviceSupportedSpecs SDL_GetCameraDeviceSupportedSpecs_REAL
 #define SDL_GetCameraDeviceName SDL_GetCameraDeviceName_REAL
+#define SDL_OpenCameraDevice SDL_OpenCameraDevice_REAL
+#define SDL_GetCameraInstanceID SDL_GetCameraInstanceID_REAL
+#define SDL_GetCameraProperties SDL_GetCameraProperties_REAL
 #define SDL_GetCameraSpec SDL_GetCameraSpec_REAL
-#define SDL_GetCameraFormat SDL_GetCameraFormat_REAL
-#define SDL_GetNumCameraFormats SDL_GetNumCameraFormats_REAL
-#define SDL_GetCameraFrameSize SDL_GetCameraFrameSize_REAL
-#define SDL_GetNumCameraFrameSizes SDL_GetNumCameraFrameSizes_REAL
-#define SDL_GetCameraStatus SDL_GetCameraStatus_REAL
-#define SDL_StartCamera SDL_StartCamera_REAL
 #define SDL_AcquireCameraFrame SDL_AcquireCameraFrame_REAL
 #define SDL_ReleaseCameraFrame SDL_ReleaseCameraFrame_REAL
-#define SDL_StopCamera SDL_StopCamera_REAL
 #define SDL_CloseCamera SDL_CloseCamera_REAL