Refactored: test scaffolding for splitting accesses to multiple buffers
IpcBuffer: a primitive value may be split over multiple buffers
IpcBuffer: check that there is no gaps in buffers - everything should work the same when the backing buffers are concatenated
Refactored: extract ByteBufferSequenceContract from AllocatedByteBufferSequenceTest
Created MappedByteBufferSequence
MappedByteBufferSequence: multiple instances/processes with same path should access same data