Separate mod menu popup creation for patching

[Septikai]

This separates out the creation of a ModsMenuPopup into a different method, allowing mods to patch it so they can display custom content and settings in their menu underneath the default content.

Example that I threw into the bottom of my InfiniteAmmo mod for testing:

[HarmonyPatch(typeof(Silk.ModsUI), nameof(ModsUI.MakePopup))]
internal class ModsMenuPatch
{
    public static void Postfix((string title, string[] authors, string version, string gameVersion, string id) mod, ref ModsMenuPopup __result)
    {
        if (mod.title != "InfiniteAmmo") return;
        __result.CreateParagraph("testing123");
    }
}

[Septikai]

This is on hold until I can get a working implementation for checkbox and slider text, which will hopefully be over the weekend/on monday