Wayland: Add support for pointer event frames

This adds support for wl_seat version 5, which adds pointer frames.
This allows two-dimensional scroll input to be emitted as single events
instead of one event per axis per motion.

It's also the the foundation for future enhancements like properly
scaled discrete scroll events and server-side key repeat.

Fixes #2494

src/wl_platform.h

@@ -414,7 +414,8 @@ typedef struct _GLFWwindowWayland
         GLFWbool                    decorations;
         struct wl_buffer*           buffer;
         _GLFWfallbackEdgeWayland    top, left, right, bottom;
-        wl_fixed_t                  pointerX, pointerY;
+        double                      pointerX, pointerY;
+        uint32_t                    buttonPressSerial;
         const char*                 cursorName;
     } fallback;
 } _GLFWwindowWayland;
@@ -472,6 +473,17 @@ typedef struct _GLFWlibraryWayland
     short int                   scancodes[GLFW_KEY_LAST + 1];
     char                        keynames[GLFW_KEY_LAST + 1][5];
 
+    struct {
+        struct wl_surface*      pointerSurface;
+        unsigned int            events;
+        double                  pointerX;
+        double                  pointerY;
+        double                  scrollX;
+        double                  scrollY;
+        int                     button;
+        int                     action;
+    } pending;
+
     struct {
         void*                   handle;
         struct xkb_context*     context;