linux: Treat fullscreen as tiled on X11 and prevent resizing while maximized (#13990)

Two quick fixes for issues I noticed:

1. Fullscreening an unmaximized X11 window still showed rounded window
corners and allowed resizing
2. Maximized windows still allowed for resizing on corners due to
missing checks

![image](https://github.com/zed-industries/zed/assets/71973804/47df4de2-4013-4e51-88c3-d33b52a909f5)


Release Notes:

- N/A

crates/workspace/src/workspace.rs

@@ -6658,7 +6658,7 @@ fn resize_edge(
 
     let corner_size = size(shadow_size * 1.5, shadow_size * 1.5);
     let top_left_bounds = Bounds::new(Point::new(px(0.), px(0.)), corner_size);
-    if top_left_bounds.contains(&pos) {
+    if !tiling.top && top_left_bounds.contains(&pos) {
         return Some(ResizeEdge::TopLeft);
     }
 
@@ -6666,7 +6666,7 @@ fn resize_edge(
         Point::new(window_size.width - corner_size.width, px(0.)),
         corner_size,
     );
-    if top_right_bounds.contains(&pos) {
+    if !tiling.top && top_right_bounds.contains(&pos) {
         return Some(ResizeEdge::TopRight);
     }
 
@@ -6674,7 +6674,7 @@ fn resize_edge(
         Point::new(px(0.), window_size.height - corner_size.height),
         corner_size,
     );
-    if bottom_left_bounds.contains(&pos) {
+    if !tiling.bottom && bottom_left_bounds.contains(&pos) {
         return Some(ResizeEdge::BottomLeft);
     }
 
@@ -6685,7 +6685,7 @@ fn resize_edge(
         ),
         corner_size,
     );
-    if bottom_right_bounds.contains(&pos) {
+    if !tiling.bottom && bottom_right_bounds.contains(&pos) {
         return Some(ResizeEdge::BottomRight);
     }