Change merge_sorter::m_finishedRuns from a stream_size_type to a memory_size_type.

On 32-bit systems, this reduces the maximum size of data we can sort to
M * 2^32. However, even for a very modest run length such as
M = 1 megabyte, we maintain support for more than a thousand terabytes
of data.
merger: Change runLength from a size_t to a stream_size_type.

We also get rid of a superfluous member variable.
Disable MSVC warning about `this` in initializer list for node constructors.

Using `this` in this context is safe, since the `node_token` will not
access members of the (at this point incompletely constructed) `node`
object.
Change sort_parameters `runLength` from a stream_size_type to a memory_size_type.

The run length must be a buffer size that we can keep in main memory, so
on 32-bit systems it does not make sense to have a runLength greater
than 2^32.
Change progress_indicator_arrow::m_indicatorLength from stream_size_type to memory_size_type.
Fix unused variable warnings in ami::stream.
Switch linear_memory_base::memory_usage from a stream_size_type to a memory_size_type.