linear Par[t] -> read Par[t] -> linear Par[t]

[kikofernandez]

A polymorphic function / method does not allow to deal with a read and linear mode at the same time. The sharable means, among other things, that it's not linear. In the current affine ParT paper, we allow linear Par[t] -> read Par[t] -> linear Par[t]. This is safe from the concurrency perspective and allows to re-use container-like data structures from the runtime, saving on allocations.