CAS-12220 : Add tests for psfmode=flat
Added a test class for the new PSF mode parameter since it is a
substantial change. The tests should cover most failure modes.
CAS-12220 : Add AWP2 support for flatPSF
AWP2 was previously gated-off because the flat PS CF kernel was being
over-written in-place by the A-term kernel, causing the flatPSF mode to
generate bit-identical PSF to the regular PSF mode.
This separates out the flat-PSF kernel from mosaic into it's own method,
and that has been hooked into AWP2.
There are still no unit tests to test this new mode, but local tests
seem to confirm that it's working (or at least not crashing...)
CAS-12220 : new psfmode argument in tclean.xml + cleanup
Add a new "psfmode" argument within tclean that triggers the gridders to
use the flatPSF path, and complete the pipes all the way down into
SynthesisImager.
The old tclean.py hack has been removed in favour of the C++
code-changes.
CAS-12220 : Fixes for AWP flatPSF path
AWP was crashing with the previous flatPSF implementation,
this cleans up some old code and fixes the flatPSF path.
AWP2 is still unsupported with these fixes, that will be looked at later
on. It raises an error if flatpsf is used in conjuction with AWP2.
