Refactor xcomposite

Move common code between cuda/vaapi implementations
into xcomposite file.
This also fixes limited/full range colors on nvidia.

include/capture/xcomposite_cuda.h

@@ -2,14 +2,10 @@
 #define GSR_CAPTURE_XCOMPOSITE_CUDA_H
 
 #include "capture.h"
-#include "../egl.h"
-#include "../vec2.h"
+#include "xcomposite.h"
 
 typedef struct {
-    gsr_egl *egl;
-    Window window;
-    bool follow_focused; /* If this is set then |window| is ignored */
-    vec2i region_size; /* This is currently only used with |follow_focused| */
+    gsr_capture_xcomposite_params base;
     bool overclock;
 } gsr_capture_xcomposite_cuda_params;