Avoid some alloc by merging where and single (#2044)

Author: SimonCropp

src/DocumentFormat.OpenXml.Framework/Validation/Semantic/RelationshipTypeConstraint.cs

@@ -63,8 +63,7 @@ public RelationshipTypeConstraint(OpenXmlQualifiedName attribute, string type)
             else
             {
                 var pair = current.Part.Parts
-                    .Where(p => p.RelationshipId == attribute.Value.InnerText)
-                    .SingleOrDefault();
+                    .SingleOrDefault(p => p.RelationshipId == attribute.Value.InnerText);
 
                 if (pair is { })
                 {

src/DocumentFormat.OpenXml.Framework/Validation/Semantic/SemanticConstraint.cs

@@ -131,8 +131,7 @@ private static void Get(ValidationContext context, out SemanticValidationLevel l
             {
                 return current.Package
                     .GetAllParts()
-                    .Where(p => p.Parts.Any(r => r.OpenXmlPart.PackagePart.Uri == current.Part.PackagePart.Uri))
-                    .First();
+                    .First(p => p.Parts.Any(r => r.OpenXmlPart.PackagePart.Uri == current.Part.PackagePart.Uri));
             }
             else
             {