You don't have to use reflection if everything is public

TheSolution.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Mono.Cecil;
using UnityEditor;
using UnityEditorInternal;

public class TheSolution
{
    [MenuItem("The Solution/Do It...")]
    public static void MakePublic()
    {
        MakeAssemblyPublic(InternalEditorUtility.GetEditorAssemblyPath());
        MakeAssemblyPublic(InternalEditorUtility.GetEngineAssemblyPath());
    }

    private static void MakeAssemblyPublic(string assemblyPath)
    {
        AssemblyDefinition assembly = AssemblyDefinition.ReadAssembly(assemblyPath);
        
        foreach(ModuleDefinition moduleDefinition in assembly.Modules)
        {
            foreach(TypeDefinition typeDefinition in moduleDefinition.Types)
            {
                typeDefinition.IsPublic = true; 

                foreach(MethodDefinition methodDefinition in typeDefinition.Methods)
                {
                    methodDefinition.IsPublic = true;
                }

                foreach(FieldDefinition fieldDefinition in typeDefinition.Fields)
                {
                    fieldDefinition.IsPublic = true;
                }

                foreach(PropertyDefinition propertyDefinition in typeDefinition.Properties)
                {
                    if(propertyDefinition.SetMethod != null)
                    {
                        propertyDefinition.SetMethod.IsPublic = true;
                    }

                    if(propertyDefinition.GetMethod != null)
                    {
                        propertyDefinition.GetMethod.IsPublic = true;
                    }
                }
            }
        }
        assembly.Write(assemblyPath);
    }
}