Add support for reading compressed NDPI tiles

[melissalinkert]

This expands on the "precompressed" features added in #3992.

The main goal was to just add compressed tile reading to the NDPI reader, so that conversion from NDPI to DICOM wouldn't require much if any recompression. This required a variety of changes not limited to NDPI though:

• update JPEGTurboService so that the repackaged compressed tiles can be retrieved, as well as the tile size and counts
• move general TIFF tile copying logic out of SVSReader, and into MinimalTiffReader (to prevent duplicate logic in NDPIReader)
  • this should also make it easier to support precompressed tiles in other TIFF-based formats later on
• update NDPIReader to report optimal sizes based on actual IFD/JPEG stream, instead of constant 1024x1024
• update DicomWriter to allow different tile sizes in each resolution, since NDPI reports different sizes per resolution
• update NDPIReader to use the saveCompressedBytes API

The end result is that something like this should now work:

bfconvert -noflat -precompressed -compression JPEG CMU-1.ndpi cmu.dcm

and should complete within a few seconds as all tiles can be copied without any recompression.

I would not expect SVS -> DICOM support to change, but it probably makes sense to double-check just in case the refactoring caused any problems.

I don't expect this to fail tests, but excluding for now so this doesn't distract from 7.3.0. Given the API changes in JPEGTurboService, this probably does require a major version.

cc @dclunie, @fedorov