Wayland: Fix key repeat on very old compositors

The client-side key repeat timer fd was only created for wl_seat version
4 or later, but was then used unconditionally during event processing.

Rather than have this mechanism do nothing in a more correct way on
wl_seat version 3 or earlier (which is very old by now), this commit
creates the key repeat timer fd and then sets (hopefully gentle)
hardcoded repeat delay and rate.

README.md

@@ -148,6 +148,7 @@ information on what to include when reporting a bug.
    potential segmentation fault (#2744)
  - [Wayland] Bugfix: Confining or disabling the cursor could segfault on
    compositors without `pointer-constraints-unstable-v1`
+ - [Wayland] Bugfix: Key repeat did not function on very old compositors
  - [X11] Bugfix: Running without a WM could trigger an assert (#2593,#2601,#2631)
  - [X11] Bugfix: Occasional crash when an idle display awakes (#2766) 
  - [X11] Bugfix: Prevent BadWindow when creating small windows with a content scale

src/wl_init.c

@@ -137,13 +137,6 @@ static void registryHandleGlobal(void* userData,
                 wl_registry_bind(registry, name, &wl_seat_interface,
                                  _glfw_min(4, version));
             _glfwAddSeatListenerWayland(_glfw.wl.seat);
-
-            if (wl_seat_get_version(_glfw.wl.seat) >=
-                WL_KEYBOARD_REPEAT_INFO_SINCE_VERSION)
-            {
-                _glfw.wl.keyRepeatTimerfd =
-                    timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC | TFD_NONBLOCK);
-            }
         }
     }
     else if (strcmp(interface, "wl_data_device_manager") == 0)
@@ -834,6 +827,16 @@ int _glfwInitWayland(void)
 
     createKeyTables();
 
+    _glfw.wl.keyRepeatTimerfd =
+        timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC | TFD_NONBLOCK);
+    if (_glfw.wl.keyRepeatTimerfd == -1)
+    {
+        _glfwInputError(GLFW_PLATFORM_ERROR,
+                        "Wayland: Failed to create timerfd: %s",
+                        strerror(errno));
+        return GLFW_FALSE;
+    }
+
     _glfw.wl.xkb.context = xkb_context_new(XKB_CONTEXT_NO_FLAGS);
     if (!_glfw.wl.xkb.context)
     {

src/wl_window.c

@@ -1942,6 +1942,13 @@ static void seatHandleCapabilities(void* userData,
     {
         _glfw.wl.keyboard = wl_seat_get_keyboard(seat);
         wl_keyboard_add_listener(_glfw.wl.keyboard, &keyboardListener, NULL);
+
+        if (wl_keyboard_get_version(_glfw.wl.keyboard) <
+            WL_KEYBOARD_REPEAT_INFO_SINCE_VERSION)
+        {
+            _glfw.wl.keyRepeatRate = 4;
+            _glfw.wl.keyRepeatDelay = 500;
+        }
     }
     else if (!(caps & WL_SEAT_CAPABILITY_KEYBOARD) && _glfw.wl.keyboard)
     {