Make private class in DV reader public (see #12358)

In order to be able to handle the DVExtHdrFields as anything
other than a string, the object will either need to be made
public or be made to implement some public API (e.g. Map).
Re-hide and flatten DVExtHdrFields

Rather than expose the inner class, we flatten
its contents into the metadata table so that consumers
need not know of its existence.
Fix import error
Correct for off-by-ones in SizeZ reporting
Merge pull request #1139 from imunro/SDT_meas_mode_0

Fix for BH .Sdt meas mode 0 & 1 single pixel files & (unrelated) problem with dividing by increment count.
merge dev_5_0 -D org: PR 1146 (bfsave: metadata improvements)
merge dev_5_0 -D org: PR 1153 (CZI: prevent AIOOB exception when populating position metadata)
merge dev_5_0 -D org: PR 1159 (First round of Nikon ND2 fixes)
merge dev_5_0 -D org: PR 1160 (Make private class in DV reader public (see #12358) (rebased onto dev_5_0))
merge dev_5_0 -D org

Repository: openmicroscopy/bioformats
Updating 623cd6d..56600f4
Merged PRs (fast-forward):
  # PR 1139 imunro 'Fix for BH .Sdt meas mode 0 & 1 single pixel files & (unrelated) problem with dividing by increment count.'
  # PR 1150 melissalinkert 'Allow dist-matlab to run on Windows (rebased onto dev_5_0)'
  # PR 1157 hflynn 'Removing dead link from Minolta-MRW format page'
  # PR 1144 hflynn 'Updating Zeiss links'
  # PR 1151 hflynn 'Comstat2 link'
  # PR 1134 sbesson 'Add prefix to zip file produced by dist-bftools target'
  # PR 1140 hflynn 'Add 'show and edit on Github' to docs side menu'
  # PR 1143 joshmoore 'Memoizer errs'

Merged PRs:
  # PR 1146 sbesson 'bfsave: metadata improvements'
  # PR 1153 melissalinkert 'CZI: prevent AIOOB exception when populating position metadata'
  # PR 1159 melissalinkert 'First round of Nikon ND2 fixes'
  # PR 1160 joshmoore 'Make private class in DV reader public (see #12358) (rebased onto dev_5_0)'

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