Fix #11308 - Add missing IN operator

Author: NathanW2

resources/function_help/IN

@@ -0,0 +1,13 @@
+<h3>IN expression</h3>
+Returns 1 if value is found within a list of values
+
+<h4>Syntax</h4>
+<pre>'a' IN ('a', 'b')</pre>
+
+<h4>Arguments</h4>
+None
+
+<h4>Example</h4>
+<pre> 'A' IN ('A','B") &rarr; returns 1 </pre>
+<pre> 'A' IN ('C','B") &rarr; returns 0 </pre>
+

src/gui/qgsexpressionbuilderwidget.cpp

@@ -72,6 +72,7 @@ QgsExpressionBuilderWidget::QgsExpressionBuilderWidget( QWidget *parent )
                 .arg( tr( "Joins two values together into a string" ) )
                 .arg( tr( "Usage" ) )
                 .arg( tr( "'Dia' || Diameter" ) ) );
+  registerItem( "Operators", "IN", " IN " );
   registerItem( "Operators", "LIKE", " LIKE " );
   registerItem( "Operators", "ILIKE", " ILIKE " );
   registerItem( "Operators", "IS", " IS " );