Refactor nvfbc into abstract capture api

include/capture/nvfbc.h

@@ -0,0 +1,17 @@
+#ifndef GSR_CAPTURE_NVFBC_H
+#define GSR_CAPTURE_NVFBC_H
+
+#include "capture.h"
+#include "../vec2.h"
+
+typedef struct {
+    const char *display_to_capture; /* if this is "screen", then the entire x11 screen is captured (all displays) */
+    int fps;
+    vec2i pos;
+    vec2i size;
+    bool direct_capture; /* temporary disabled */
+} gsr_capture_nvfbc_params;
+
+gsr_capture* gsr_capture_nvfbc_create(const gsr_capture_nvfbc_params *params);
+
+#endif /* GSR_CAPTURE_NVFBC_H */