Support data quality and schema migration rules for net462 (#2514)

Author: rayokota

src/Confluent.SchemaRegistry.Rules/BuiltinLibrary.cs

@@ -7,15 +7,15 @@ public class BuiltinLibrary : ILibrary
 
         public virtual IList<EnvOption> CompileOptions
         {
-            get => new List<EnvOption> { IEnvOption.Declarations(BuiltinDeclarations.Create()) };
+            get => new List<EnvOption> { EnvOptions.Declarations(BuiltinDeclarations.Create()) };
         }
 
         public virtual IList<ProgramOption> ProgramOptions
         {
             get => new List<ProgramOption>
             {
-                IProgramOption.EvalOptions(EvalOption.OptOptimize),
-                IProgramOption.Functions(BuiltinOverload.Create())
+                Cel.ProgramOptions.EvalOptions(EvalOption.OptOptimize),
+                Cel.ProgramOptions.Functions(BuiltinOverload.Create())
             };
         }
     }

src/Confluent.SchemaRegistry.Rules/CompilerServices.cs

@@ -0,0 +1,23 @@
+// Copyright 2024 Confluent Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Refer to LICENSE for more information.
+
+using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    internal static class IsExternalInit { }
+}

src/Confluent.SchemaRegistry.Rules/Confluent.SchemaRegistry.Rules.csproj

@@ -16,7 +16,7 @@
         <Title>Confluent.SchemaRegistry.Rules</Title>
         <AssemblyName>Confluent.SchemaRegistry.Rules</AssemblyName>
         <VersionPrefix>2.11.1</VersionPrefix>
-        <TargetFrameworks>net6.0;net8.0</TargetFrameworks>
+        <TargetFrameworks>netstandard2.1;net462;net6.0;net8.0</TargetFrameworks>
         <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
         <GenerateDocumentationFile>true</GenerateDocumentationFile>
         <SignAssembly>true</SignAssembly>
@@ -34,7 +34,7 @@
     </ItemGroup>
 
     <ItemGroup>
-      <PackageReference Include="Cel.NET" Version="0.3.2" />
+      <PackageReference Include="Cel.NET" Version="0.4.0" />
     </ItemGroup>
 
     <ItemGroup>