Fix ComboBox height clipping under text scaling

[Copilot]

ComboBox used a fixed item height, so larger system text scaling could clip the selected value in the closed control. This updates ComboBox sizing to behave like other input controls by allowing vertical growth with scaled text.

• Root cause

  • ComboBox button content was constrained by a fixed height in _ComboBoxItemContainer, which did not adapt when text metrics increased.

• Implementation

  • Replaced fixed height with a minimum-height constraint in _ComboBoxItemContainer.
  • Preserves baseline compact sizing while allowing the control to expand when scaled text requires more vertical space.

• Regression coverage

  • Added a widget test that compares ComboBox height at TextScaler.linear(1) vs TextScaler.linear(2) and asserts the scaled case is taller.

• Changelog

  • Added a [next] changelog entry documenting ComboBox text-scaling height behavior.

return Container(
  constraints: BoxConstraints(
    minHeight: hasPadding
        ? adjustedItemHeight
        : (adjustedItemHeight - _kMenuItemBottomPadding).clamp(
            0.0,
            double.infinity,
          ),
  ),
  alignment: AlignmentDirectional.centerStart,
  child: ...
);

• Fixes 🐛 ComboBox doesn't take textScaler in account #1342

[bdlukaa]

@copilot Use MediaQuery.textScalerOf(context).scale instead of dynamic height because the each tile inside the combo box overlay should have the same height as the button.

[Copilot]

@copilot Use MediaQuery.textScalerOf(context).scale instead of dynamic height because the each tile inside the combo box overlay should have the same height as the button.

Updated in 4975aac. _ComboBoxItemContainer now uses MediaQuery.textScalerOf(context).scale(...) for both menu-item and button heights, replacing the intrinsic/dynamic height approach.