Check for wrapper types in C# code gen should be case insensitive

What version of protobuf and what language are you using?
Version: Gprc.Tools version 2.71.0
Language: C#

What operating system (Linux, Windows, ...) and version?

Windows

What runtime / compiler are you using (e.g., python version or gcc version)

What did you do?

Have a proto file like this:

syntax = "proto3";

option csharp_namespace = "Microsoft.AspNetCore.Grpc.JsonTranscoding.Tests.TestObjects.ProtobutMessages";

import "Google/protobuf/wrappers.proto"; 
import "Google/api/annotations.proto"; 

package test;

message WrappersMessage {
    google.protobuf.StringValue string_value = 1;
    google.protobuf.Int32Value int32_value = 2;
    google.protobuf.Int64Value int64_value = 3;
    google.protobuf.FloatValue float_value = 4;
    google.protobuf.DoubleValue double_value = 5;
    google.protobuf.BoolValue bool_value = 6;
    google.protobuf.UInt32Value uint32_value = 7;
    google.protobuf.UInt64Value uint64_value = 8;
    google.protobuf.BytesValue bytes_value = 9;
}

It successfully compiles, but the properties generated on the C# type are StringValue rather than string.

This is because the import isn't completely lower case: import "Google/protobuf/wrappers.proto";. The code to detect if a field is a wrapper then checks the file name without ignoring case:

https://github.com/protocolbuffers/protobuf/blob/8228ee42b512cc330971e61bc9b86935a59f3477/src/google/protobuf/compiler/csharp/csharp_helpers.h#L112-L115

What did you expect to see

string field:

/// <summary>Field number for the "string_value" field.</summary>
public const int StringValueFieldNumber = 1;
private static readonly pb::FieldCodec<string> _single_stringValue_codec = pb::FieldCodec.ForClassWrapper<string>(10);
private string stringValue_;
[global::System.Diagnostics.DebuggerNonUserCodeAttribute]
[global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
public string StringValue {
  get { return stringValue_; }
  set {
    stringValue_ = value;
  }
}

What did you see instead?

StringValue field:

/// <summary>Field number for the "string_value" field.</summary>
public const int StringValueFieldNumber = 1;
private global::Google.Protobuf.WellKnownTypes.StringValue stringValue_;
[global::System.Diagnostics.DebuggerNonUserCodeAttribute]
[global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
public global::Google.Protobuf.WellKnownTypes.StringValue StringValue {
  get { return stringValue_; }
  set {
    stringValue_ = value;
  }
}

Anything else we should know about your project / environment

Start with src/google/protobuf/compiler/csharp/csharp_helpers.h at the wrapper-type detection around lines 112-115, then reproduce the case-sensitive import using the proto shown in the issue. Verify the C# generator recognizes Google/protobuf/wrappers.proto regardless of import casing and produces the primitive string property shown under the expected output.