`linearizing_input_stream` allows transparently reading linearized
values from a fragmented buffer. This is done by linearizing on-the-fly
only those read values that happen to be split across multiple
fragments. This reduces the size of the largest allocation from the size
of the entire buffer (when the entire buffer is linearized) to the size
of the largest read value. This is a huge gain when the buffer contains
loads of small objects, and modest gains when the buffer contains few
large objects. But the even in the worst case the size of the largest
allocation will be less or equal compared to the case where the entire
buffer is linearized.
This stream is planned to be used as glue code between the fragmented
cell value and the collection deserialization code which expects to be
reading linearized values.
