Do not round panel rectangles to pixel grid (#5196)

* Closes #5173
* Part of #5163
* Related to #5164

crates/egui/src/containers/panel.rs

@@ -329,9 +329,6 @@ impl SidePanel {
             ui.ctx().set_cursor_icon(cursor_icon);
         }
 
-        // Keep this rect snapped so that panel content can be pixel-perfect
-        let rect = ui.painter().round_rect_to_pixels(rect);
-
         PanelState { rect }.store(ui.ctx(), id);
 
         {
@@ -824,9 +821,6 @@ impl TopBottomPanel {
             ui.ctx().set_cursor_icon(cursor_icon);
         }
 
-        // Keep this rect snapped so that panel content can be pixel-perfect
-        let rect = ui.painter().round_rect_to_pixels(rect);
-
         PanelState { rect }.store(ui.ctx(), id);
 
         {
@@ -842,6 +836,8 @@ impl TopBottomPanel {
             };
             // TODO(emilk): draw line on top of all panels in this ui when https://github.com/emilk/egui/issues/1516 is done
             let resize_y = side.opposite().side_y(rect);
+
+            // This makes it pixel-perfect for odd-sized strokes (width=1.0, width=3.0, etc)
             let resize_y = ui.painter().round_to_pixel_center(resize_y);
 
             // We want the line exactly on the last pixel but rust rounds away from zero so we bring it back a bit for