Add identifier for internal attribute for exclude by some methods

[baumannsven]

This feature is useful for better work with virtual attribute.
Virtual attribute has problem if we get parse values from item.
You can see this by attribute_file by the virtual FileOrder.

[richardhj]

Can we find another name than IVirtual? IMHO it is hard to catch, what a "virtual attribute" is.
Or at least adjust the description

Interface for "virtual" MetaModel attributes.
This interface is helper for check if the attribute is virtual.

[discordier]

I am with @richardhj on this one. We might want to change the name to something else IInternal would IMO re ensemble unrenderable and unmodifyable attributes more closely.
In the end, we should rethink what types of attributes we really have in addition to the current ones.

Finally I do not understand why "virtual" attributes should get excluded from rendering.

[baumannsven]

The IVirtual name comes from logic exception who throw by attribute_file.
What ist the problem for the name of this interface? Can you tell me why?

https://github.com/MetaModels/attribute_file/blob/hotfix/order-field/src/MetaModels/Attribute/File/FileOrder.php#L101

[discordier]

The problem is only with the naming. In the end, almost all attributes are "virtual" because they are not part of the "entity" but only added.
MetaModels is sort of an EAV system where all attributes are "virtual", having some of them now named "virtual" does not help and therefore we are searching for a better name.

[baumannsven]

Now i understood the naming for this interface. I rename this interface.

[zonky2]

IInternal

[baumannsven]

I have switch the interface name from IVirtual to IInternal,