Fix delegate allocation in CachingContext.GetOrAddJsonTypeInfo (#80437)

* Fix delegate allocation in CachingContext.GetOrAddJsonTypeInfo

* Address PR feedback

Author: stephentoub

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Caching.cs

@@ -156,11 +156,14 @@ internal void ClearCaches()
         internal sealed class CachingContext
         {
             private readonly ConcurrentDictionary<Type, JsonTypeInfo?> _jsonTypeInfoCache = new();
+            private readonly Func<Type, JsonTypeInfo?> _jsonTypeInfoFactory;
 
             public CachingContext(JsonSerializerOptions options, int hashCode)
             {
                 Options = options;
                 HashCode = hashCode;
+
+                _jsonTypeInfoFactory = options.GetTypeInfoNoCaching;
             }
 
             public JsonSerializerOptions Options { get; }
@@ -169,7 +172,8 @@ public CachingContext(JsonSerializerOptions options, int hashCode)
             // If changing please ensure that src/ILLink.Descriptors.LibraryBuild.xml is up-to-date.
             public int Count => _jsonTypeInfoCache.Count;
 
-            public JsonTypeInfo? GetOrAddJsonTypeInfo(Type type) => _jsonTypeInfoCache.GetOrAdd(type, Options.GetTypeInfoNoCaching);
+            public JsonTypeInfo? GetOrAddJsonTypeInfo(Type type) => _jsonTypeInfoCache.GetOrAdd(type, _jsonTypeInfoFactory);
+
             public bool TryGetJsonTypeInfo(Type type, [NotNullWhen(true)] out JsonTypeInfo? typeInfo) => _jsonTypeInfoCache.TryGetValue(type, out typeInfo);
 
             public void Clear()