use ScanExtented in ConvertNumComponentsToOffsets

Fixes: #424 (closed)

ConvertNumComponentsToOffsets using ScanExtented vs. ScanExclusive

This commit also:
- Removes a corner case not longer used at ArrayPortalGroupVecVariable::get
- Changes doc regarding the number of offset elements in the input
  array handler of ConvertNumComponentsToOffsets.
- Updates invokation of make_ArrayGroupVectVariable in multiple files
- Adds its corresponding changelog entry