Restore windows after fullscreen

Store position and size of windows before going fullscreen. This is more
efficient than arrange() and also works with floating windows

All the clients keep their original position because arrange() isn't
used after quitting fullscreen

dwl.c

@@ -112,6 +112,10 @@ typedef struct {
 	unsigned int tags;
 	int isfloating;
 	uint32_t resize; /* configure serial of a pending resize */
+	int prevx;
+	int prevy;
+	int prevwidth;
+	int prevheight;
 } Client;
 
 typedef struct {
@@ -1048,6 +1052,16 @@ fullscreenotify(struct wl_listener *listener, void *data) {
 	wlr_xdg_toplevel_set_fullscreen(
 			c->surface.xdg, !c->surface.xdg->toplevel->current.fullscreen);
 	c->bw = (int)c->surface.xdg->toplevel->current.fullscreen * borderpx;
+
+	if (c->surface.xdg->toplevel->current.fullscreen) { /* fullscreen off */
+		resize(c, c->prevx, c->prevy, c->prevwidth, c->prevheight, 0);
+	} else { /* fullscreen on */
+		c->prevx = c->geom.x;
+		c->prevy = c->geom.y;
+		c->prevheight = c->geom.height;
+		c->prevwidth = c->geom.width;
+		resize(c, c->mon->w.x, c->mon->w.y, c->mon->w.width, c->mon->w.height, 0);
+	}
 }
 
 Monitor *