OS provider should support shared memory allocations

[bratpiorka]

Rationale

OS Memory Provider should support shared memory allocations. This could be useful in scenarios, where there are two or more processes and the memory allocated in the first process is needed in the second process.

API Changes

To support shared memory, OS Memory Provider should accept new flag UMF_MEM_MAP_SHARED/PRIVATE.
In case of SHARED allocations, mmap should use file descriptor got from memfd.

OS Memory Provider should also implement IPC API.

[bratpiorka]

draft PR with changes: #429

[bratpiorka]

closed by #429