Added GM:OnDuplicated(ent, entDupeTable), GMod PR

[Grocel]

In adjacent to: Facepunch/garrysmod#2408

Works like ENTITY:OnDuplicated(ent, entDupeTable) but doesn't require adding/detouring ent.OnDuplicated on OnEntityCreated calls for addon-foreign entities.

This adds a easy way to add generic logic early to the duplication life cycle. It is called a way before duplicator.RegisterEntityModifier() added callers are being iterated. The new hook also reduces the risk of conflicts caused by detours of pre-existing ent.OnDuplicated code.

Test script:

if SERVER then
    hook.Add("OnDuplicated", "Test", function(ent, entTable)
        print(ent)
        PrintTable(entTable)
    end)
end

[Grocel]

The linter results are not relevant to my changes, so I can't fix them.

[Astralcircle]

I don't see any point in merging this until it's merged into GMOD. Because very few addons rely on the AdvDupe2 duplicator specifically