Simplify swap BodyClauses logic in LINQ Visitors (#2379)

Author: bahusoid

src/NHibernate/Linq/GroupBy/AggregatingGroupByRewriter.cs

@@ -83,8 +83,7 @@ private static void FlattenSubQuery(QueryModel queryModel, QueryModel subQueryMo
 				var whereClause = clause as WhereClause;
 				if (whereClause != null)
 				{
-					queryModel.BodyClauses.RemoveAt(i);
-					queryModel.BodyClauses.Insert(i, new NhHavingClause(whereClause.Predicate));
+					queryModel.BodyClauses[i] = new NhHavingClause(whereClause.Predicate);
 				}
 			}
 

src/NHibernate/Linq/GroupJoin/NonAggregatingGroupJoinRewriter.cs

@@ -114,8 +114,7 @@ private void SwapClause(IBodyClause oldClause, IBodyClause newClause)
 			{
 				if (_model.BodyClauses[i] == oldClause)
 				{
-					_model.BodyClauses.RemoveAt(i);
-					_model.BodyClauses.Insert(i, newClause);
+					_model.BodyClauses[i] = newClause;
 				}
 			}
 		}

src/NHibernate/Linq/ReWriters/MoveOrderByToEndRewriter.cs

@@ -14,11 +14,10 @@ public static void ReWrite(QueryModel queryModel)
 			int len = queryModel.BodyClauses.Count;
 			for(int i=0; i<len; i++)
 			{
-				if (queryModel.BodyClauses[i] is OrderByClause)
+				if (queryModel.BodyClauses[i] is OrderByClause clause)
 				{
 					// If we find an order by clause, move it to the end of the list.
 					// This preserves the ordering of multiple orderby clauses if there are any.
-					IBodyClause clause = queryModel.BodyClauses[i];
 					queryModel.BodyClauses.RemoveAt(i);
 					queryModel.BodyClauses.Add(clause);
 					i--;

src/NHibernate/Linq/Visitors/LeftJoinRewriter.cs

@@ -43,8 +43,7 @@ public override void VisitAdditionalFromClause(AdditionalFromClause fromClause,
 
 			queryModel.TransformExpressions(ex => ReferenceReplacingExpressionVisitor.ReplaceClauseReferences(ex, innerSelectorMapping, false));
 
-			queryModel.BodyClauses.RemoveAt(index);
-			queryModel.BodyClauses.Insert(index, @join);
+			queryModel.BodyClauses[index] = @join;
 			InsertBodyClauses(subQueryModel.BodyClauses.Where(b => !(b is WhereClause)), queryModel, index + 1);
 
 			var innerBodyClauseMapping = new QuerySourceMapping();
@@ -68,4 +67,4 @@ private static bool IsLeftJoin(QueryModel subQueryModel)
 				   subQueryModel.ResultOperators[0] is DefaultIfEmptyResultOperator;
 		}
 	}
-}
+}