strech all flexible wigets, not just dividers

Signed-off-by: Bruno Rino <bruno.rino@gmail.com>

src/cocoa/toga_cocoa/widgets/divider.py

@@ -1,3 +1,5 @@
+from travertino.size import at_least
+
 from toga_cocoa.libs import NSBox, NSBoxType
 
 from .base import Widget
@@ -16,9 +18,9 @@ def rehint(self):
 
         if self.interface.direction == self.interface.VERTICAL:
             self.interface.intrinsic.width = content_size.width
-            self.interface.intrinsic.height = 0
+            self.interface.intrinsic.height = at_least(content_size.height)
         else:
-            self.interface.intrinsic.width = 0
+            self.interface.intrinsic.width = at_least(content_size.width)
             self.interface.intrinsic.height = content_size.height
 
     def set_direction(self, value):

src/core/toga/style/pack.py

@@ -27,7 +27,7 @@
 )
 from travertino.declaration import BaseStyle, Choices
 from travertino.layout import BaseBox
-from travertino.size import BaseIntrinsicSize
+from travertino.size import BaseIntrinsicSize, at_least
 
 from toga.fonts import SYSTEM_DEFAULT_FONT_SIZE, Font
 
@@ -321,9 +321,9 @@ def _layout_row_children(self, node, available_width, available_height, scale):
                 )
                 height = max(height, child_height)
 
-        # Pass 4: set vertical position of each child.
+        # Pass 4: set vertical position of each child, and extend flexible children to the full height.
         for child in node.children:
-            if not self.height and not child.intrinsic.height:
+            if child.style.flex or type(child.intrinsic.height) is at_least:
                 child.layout.content_height = (
                     height
                     - scale(child.style.padding_top)
@@ -467,9 +467,9 @@ def _layout_column_children(self, node, available_width, available_height, scale
             )
             width = max(width, child_width)
 
-        # Pass 4: set horizontal position of each child.
+        # Pass 4: set horizontal position of each child, and extend flexible children to full width.
         for child in node.children:
-            if not self.width and not child.intrinsic.width:
+            if child.style.flex or type(child.intrinsic.width) is at_least:
                 child.layout.content_width = (
                     width
                     - scale(child.style.padding_left)