Ensure panel and pane sizes are integral (#8619)

Fixes: #8050

For some reason that we didn't investigate, if you have view caching
enabled,
and you have non-integer sized bounds, and you are right aligning
things, the
co-ordinates can differ by +/- 1px when using the cached view.

The easiest fix for now is to just not do that.

Co-Authored-By: Antonio <as-cii@zed.dev>

Release Notes:

- Fixed the pane icons flickering
([#8050](https://github.com/zed-industries/zed/issues/8050)).

Co-authored-by: Antonio <as-cii@zed.dev>

crates/workspace/src/pane_group.rs

@@ -883,7 +883,8 @@ mod element {
 
                 let child_size = bounds
                     .size
-                    .apply_along(self.axis, |_| space_per_flex * child_flex);
+                    .apply_along(self.axis, |_| space_per_flex * child_flex)
+                    .map(|d| d.round());
 
                 let child_bounds = Bounds {
                     origin,