[layout][ux] Avoid too short variable editor in layout properties

on hi-dpi displays

(cherry picked from commit ac9a4ef)

Author: nyalldawson

src/app/layout/qgslayoutpropertieswidget.cpp

@@ -31,6 +31,8 @@ QgsLayoutPropertiesWidget::QgsLayoutPropertiesWidget( QWidget *parent, QgsLayout
   setPanelTitle( tr( "Layout Properties" ) );
   blockSignals( true );
 
+  mVariableEditor->setMinimumHeight( mVariableEditor->fontMetrics().height() * 15 );
+
   updateSnappingElements();
 
   mGridSpacingUnitsCombo->linkToWidget( mGridResolutionSpinBox );

src/gui/layout/qgslayoutitemwidget.cpp

@@ -228,6 +228,8 @@ QgsLayoutItemPropertiesWidget::QgsLayoutItemPropertiesWidget( QWidget *parent, Q
 {
   setupUi( this );
 
+  mVariableEditor->setMinimumHeight( mVariableEditor->fontMetrics().height() * 15 );
+
   mItemRotationSpinBox->setClearValue( 0 );
   mStrokeUnitsComboBox->linkToWidget( mStrokeWidthSpinBox );
   mStrokeUnitsComboBox->setConverter( &item->layout()->renderContext().measurementConverter() );