macOS: Display the newly created OS window in specified state

Fix the maximized window can't occupy full screen space when window
decoration or title bar is hidden.
Fix resize_in_steps being applied even when window is maximized.
Allows to specify `os_window_state` in startup session file.

kitty/state.h

@@ -15,6 +15,7 @@
 typedef enum { LEFT_EDGE, TOP_EDGE, RIGHT_EDGE, BOTTOM_EDGE } Edge;
 typedef enum { RESIZE_DRAW_STATIC, RESIZE_DRAW_SCALED, RESIZE_DRAW_BLANK, RESIZE_DRAW_SIZE } ResizeDrawStrategy;
 typedef enum { REPEAT_MIRROR, REPEAT_CLAMP, REPEAT_DEFAULT } RepeatStrategy;
+typedef enum { WINDOW_NORMAL, WINDOW_FULLSCREEN, WINDOW_MAXIMIZED, WINDOW_MINIMIZED } WindowState;
 
 typedef struct {
     char_type string[16];