Deprecate charmods callback

include/GLFW/glfw3.h

@@ -1384,6 +1384,8 @@ typedef void (* GLFWcharfun)(GLFWwindow*,unsigned int);
  *  @sa @ref input_char
  *  @sa @ref glfwSetCharModsCallback
  *
+ *  @deprecated Scheduled for removal in version 4.0.
+ *
  *  @since Added in version 3.1.
  *
  *  @ingroup input
@@ -4119,6 +4121,8 @@ GLFWAPI GLFWcharfun glfwSetCharCallback(GLFWwindow* window, GLFWcharfun cbfun);
  *  @return The previously set callback, or `NULL` if no callback was set or an
  *  [error](@ref error_handling) occurred.
  *
+ *  @deprecated Scheduled for removal in version 4.0.
+ *
  *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED.
  *
  *  @thread_safety This function must only be called from the main thread.