Improve context menu aside layout via custom logic (#22154)

* Presence of the aside no longer affects position or size of the
context menu.

* Prefers to fit to the right, then on same side of line, then other
side of line, within the following preference order:
  - Max possible size within text area.
  - Max possible size within window.
- Actual size within window. This is the only case that could cause it
to jump around with less stability.

A further enhancement atop this might be to dynamically resize aside
height to fit.

Release notes are N/A as they are covered by the notes for #22102.

Closes #8523

Release Notes:

* N/A

crates/gpui/src/geometry.rs

@@ -1003,6 +1003,18 @@ where
             size: self.size.clone() + size(double_amount.clone(), double_amount),
         }
     }
+
+    /// Extends the bounds different amounts in each direction.
+    pub fn extend(&self, amount: Edges<T>) -> Bounds<T> {
+        Bounds {
+            origin: self.origin.clone() - point(amount.left.clone(), amount.top.clone()),
+            size: self.size.clone()
+                + size(
+                    amount.left.clone() + amount.right.clone(),
+                    amount.top.clone() + amount.bottom.clone(),
+                ),
+        }
+    }
 }
 
 impl<T> Bounds<T>
@@ -1097,6 +1109,21 @@ impl<T: Clone + Default + Debug + PartialOrd + Add<T, Output = T> + Sub<Output =
     }
 }
 
+impl<T> Bounds<T>
+where
+    T: Clone + Debug + Add<T, Output = T> + Sub<T, Output = T> + Default,
+{
+    /// Computes the space available within outer bounds.
+    pub fn space_within(&self, outer: &Self) -> Edges<T> {
+        Edges {
+            top: self.top().clone() - outer.top().clone(),
+            right: outer.right().clone() - self.right().clone(),
+            bottom: outer.bottom().clone() - self.bottom().clone(),
+            left: self.left().clone() - outer.left().clone(),
+        }
+    }
+}
+
 impl<T, Rhs> Mul<Rhs> for Bounds<T>
 where
     T: Mul<Rhs, Output = Rhs> + Clone + Default + Debug,