Reduce allocations for SdkResolverService (#11803)

Author: Erarndt

src/Build/BackEnd/Components/SdkResolution/SdkResolverService.cs

@@ -226,7 +226,7 @@ private SdkResult ResolveSdkUsingResolversWithPatternsFirst(int submissionId, Sd
             resolvers = GetResolvers(
                 _generalResolversManifestsRegistry,
                 loggingContext,
-                sdkReferenceLocation).ToList();
+                sdkReferenceLocation);
 
             if (TryResolveSdkUsingSpecifiedResolvers(
                 resolvers,
@@ -274,16 +274,14 @@ private List<SdkResolver> GetResolvers(IReadOnlyList<SdkResolverManifest> resolv
             List<SdkResolver> resolvers = new List<SdkResolver>();
             foreach (var resolverManifest in resolversManifests)
             {
-                if (!_manifestToResolvers.TryGetValue(resolverManifest, out IReadOnlyList<SdkResolver> newResolvers))
+                IReadOnlyList<SdkResolver> newResolvers;
+                lock (_lockObject)
                 {
-                    lock (_lockObject)
+                    if (!_manifestToResolvers.TryGetValue(resolverManifest, out newResolvers))
                     {
-                        if (!_manifestToResolvers.TryGetValue(resolverManifest, out newResolvers))
-                        {
-                            // Loading of the needed resolvers.
-                            newResolvers = _sdkResolverLoader.LoadResolversFromManifest(resolverManifest, sdkReferenceLocation);
-                            _manifestToResolvers[resolverManifest] = newResolvers;
-                        }
+                        // Loading of the needed resolvers.
+                        newResolvers = _sdkResolverLoader.LoadResolversFromManifest(resolverManifest, sdkReferenceLocation);
+                        _manifestToResolvers[resolverManifest] = newResolvers;
                     }
                 }