IsA, ClassName & Parent should work if an instance is already destroyed

[sasial-dev]

Initially from how the following errors:

print("Removing scripts...")
for _,v in place:GetService("Workspace"):GetDescendants() do
    if v:IsA("LuaSourceContainer") then
        v:Destroy()
    end
end

I tried to get name to work as well but I couldn't unless we add a field to the Instance struct.
I also tested the other methods to see if I could remove the ensure_not_destroyed requirement but I couldn't. It might be worth documenting that lune is different to Roblox where:

local p = Instance.new("Part");
p:Destroy();
print(p:GetChildren())

returns {}

This also introduces the fact that v.Parent can = nil which is useful in telling if an Instance is destroyed.

[filiptibell]

Nice, yeah we should definitely try to be as close to Roblox behavior as possible and erroring on these was overly cautious. LGTM!