add `JUSTContext.RegisterCustomFunction(string methodAlias, Delegate method)`

[naratteu]

I'm using the following code instead of RegisterCustomFunction to leverage JUST.net in a C# REPL environment.

#r "nuget: JUST.net, 4.4.1"
using JUST;
using System.Reflection;
var context = new JUSTContext();
var dict = typeof(JUSTContext).GetField("_customFunctions", BindingFlags.NonPublic | BindingFlags.Instance)?.GetValue(context) as Dictionary<string, MethodInfo>;
var func = () => "Hello";
dict["custom"] = func.Method;
new JsonTransformer(context).Transform("""{a:"#custom()"}""", "") // {"a":"Hello"}

I don't want there to be a dynamic loading from the file system when adding custom functions.

[naratteu]

Using the hack below, I managed to utilize a closure function as a custom function.

That said, I think the library itself requires improvements instead of depending on this workaround.

#r "nuget: JUST.net, 4.4.1"
using JUST;
using System.Reflection;
using System.Globalization;

class DelegateInfo(Delegate del) : MethodInfo
{
    public override MethodAttributes Attributes => MethodAttributes.Static; // For IsStatic
    public override ParameterInfo[] GetParameters() => del.Method.GetParameters();// throw new NotImplementedException();
    public override object? Invoke(object? obj, BindingFlags invokeAttr, Binder? binder, object?[]? parameters, CultureInfo? culture) => del.DynamicInvoke(args: parameters);

    public override Type? DeclaringType => throw new NotImplementedException();
    public override ICustomAttributeProvider ReturnTypeCustomAttributes => throw new NotImplementedException();
    public override RuntimeMethodHandle MethodHandle => throw new NotImplementedException();
    public override string Name => throw new NotImplementedException();
    public override Type? ReflectedType => throw new NotImplementedException();
    public override MethodInfo GetBaseDefinition() => throw new NotImplementedException();
    public override object[] GetCustomAttributes(bool inherit) => throw new NotImplementedException();
    public override object[] GetCustomAttributes(Type attributeType, bool inherit) => throw new NotImplementedException();
    public override MethodImplAttributes GetMethodImplementationFlags() => throw new NotImplementedException();
    public override bool IsDefined(Type attributeType, bool inherit) => throw new NotImplementedException();
}

var context = new JUSTContext();
var dict = typeof(JUSTContext).GetField("_customFunctions", BindingFlags.NonPublic | BindingFlags.Instance)?.GetValue(context) as Dictionary<string, MethodInfo>;

var c = 1;
var met = dict["custom"] = new DelegateInfo((int a)=>a + c++);
var jtf = new JsonTransformer(context);
Console.WriteLine(jtf.Transform("'#custom(100)'", ""));
Console.WriteLine(jtf.Transform("{arr:['#custom()','#custom()','#custom()']}", ""));

101
{"arr":[2,3,4]}