Revert Enumerable.Repeat(value, 1) -> EnumerableUtils.One

repeat enumerator is more efficient because it takes into account number of repeats
as actual count of items in produced sequence

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Providers/MultischemaMappingResolver.cs

@@ -55,7 +55,7 @@ public override IEnumerable<SqlExtractionTask> GetSchemaTasks()
 
     public override IEnumerable<SqlExtractionTask> GetMetadataTasks()
     {
-      return EnumerableUtils.One(metadataTask);
+      return Enumerable.Repeat(metadataTask, 1);
     }
 
     private string FormatNodeName(string mappingSchema, string mappingName)

Orm/Xtensive.Orm/Orm/Providers/SimpleMappingResolver.cs

@@ -41,12 +41,12 @@ public override MappingResolveResult Resolve(SchemaExtractionResult model, strin
 
     public override IEnumerable<SqlExtractionTask> GetSchemaTasks()
     {
-      return EnumerableUtils.One(extractionTask);
+      return Enumerable.Repeat(extractionTask, 1);
     }
 
     public override IEnumerable<SqlExtractionTask> GetMetadataTasks()
     {
-      return EnumerableUtils.One(extractionTask);
+      return Enumerable.Repeat(extractionTask, 1);
     }
 
     // Constructors

Orm/Xtensive.Orm/Orm/Providers/SqlCompiler.Helpers.cs

@@ -29,7 +29,7 @@ protected SqlProvider CreateProvider(SqlSelect statement,
     protected SqlProvider CreateProvider(SqlSelect statement, QueryParameterBinding extraBinding,
       CompilableProvider origin, params ExecutableProvider[] sources)
     {
-      var extraBindings = extraBinding!=null ? EnumerableUtils.One(extraBinding) : null;
+      var extraBindings = extraBinding!=null ? Enumerable.Repeat(extraBinding, 1) : null;
       return CreateProvider(statement, extraBindings, origin, sources);
     }
 

Orm/Xtensive.Orm/Orm/Providers/StorageSequenceAccessor.cs

@@ -37,7 +37,7 @@ public Segment<long> NextBulk(SequenceInfo sequenceInfo, Session session)
 
       long hiValue = Execute(query, session);
       if (executionFromUpgrade && !hasAISettingsInMemory)
-        CleanUp(EnumerableUtils.One(sequenceInfo), session);
+        CleanUp(Enumerable.Repeat(sequenceInfo, 1), session);
 
       var increment = sequenceInfo.Increment;
       var current = hasArbitaryIncrement ? hiValue - increment : (hiValue - 1) * increment;