Unshare workaround attributes

Found with the following command:

    grep -r 'shared[^=]*_;' source/ceylon/ast/core/
Rename {Iterable,Tuple}.arguments to argumentList

Now that we have the node type Arguments (abstract supertype of
PositionalArguments, NamedArguments) in addition to ArgumentList, this
is needed to avoid confusion.
Fix #42: Editor doesn’t do a deep copy
source-gen: Fix #42: Editor doesn’t do a deep copy