Allow static method injection

[limoka]

This PR enables static methods to be injected. This mostly allows to pass such methods to il2cpp delegates, which can be useful in some cases.

My main use of this is for interacting with Burst compiler. It expects us to pass delegates pointing to valid il2cpp methods to consider them for Burst compilation.

I have tested these changes on Core Keeper Unity 2021.3.14.

[js6pak]

My test code:

public class Test : Il2CppSystem.Object
{
    public Test() : base(ClassInjector.DerivedConstructorPointer<Test>())
    {
        ClassInjector.DerivedConstructorBody(this);
    }

    public void InstanceFoo(int a, int b)
    {
        System.Console.WriteLine($"InstanceFoo {a} {b}");
    }

    public static void StaticFoo(int a, int b)
    {
        System.Console.WriteLine($"StaticFoo {a} {b}");
    }
}

ClassInjector.RegisterTypeInIl2Cpp<Test>();
var type = Il2CppType.Of<Test>();
var methods = type.GetMethods(BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);
foreach (var methodInfo in methods)
{
    Log.LogWarning(methodInfo.Name);
    if (methodInfo.Name.EndsWith("Foo"))
    {
        var o = methodInfo.IsStatic ? null : new Test();
        methodInfo.Invoke(o, new Il2CppReferenceArray<Object>([1, 2]));
    }
}