Apply DBR_VFIELD

[mdavidsaver]

Make use of DBR_VFIELD API added by epics-base/epics-base#154

Updates QSRV to...

• Map new dbCommon fields AMSG and UTAG to PVD equivalents
• handle DBR_VFIELD complex field types which are PVStructure or shared_vector<const void>.
• Add new record types
  • svectorin / svectorout where VAL is a shared_vector exposed as NTScalarArray, allowing large arrays to be moved in/out by reference.
  • ndain a special case of svectorin where VAL is a pixel array exposed as NTNDArray, with additional fields describing image shape.
  • columnarin / columnarout where VAL is an PVStructure conforming to NTTable.
  • statBin a special case of columnarin to publish statistics computed either by software (via DTYP="Soft Channel") or hardware (via. custom device support).
  • tableAgg Helper to build NTTable by concatenation of column vectors.

[AppVeyorBot]

✅ Build pva2pva 1.0.30 completed (commit 09771db485 by @mdavidsaver)

[AppVeyorBot]

✅ Build pva2pva 1.0.33 completed (commit 09771db485 by @mdavidsaver)

[mdavidsaver]

Updated after extracting and separately merging the UTAG handling as 5a81763

[AppVeyorBot]

✅ Build pva2pva 1.0.36 completed (commit 750cd51ad8 by @mdavidsaver)

[AppVeyorBot]

✅ Build pva2pva 1.0.39 completed (commit 750cd51ad8 by @mdavidsaver)