DDCore: move create_segmentation to header file so it can be used outside of DD4hep

[andresailer]

@MarkusFrankATcernch as far as I can tell this is needed to be able to do

#include "DD4hep/detail/SegmentationsInterna.h"
//....
DECLARE_SEGMENTATION(GridDRcalo, create_segmentation<dd4hep::DDSegmentation::GridDRcalo>)

for #815
So that the segmentation_constructor is created and part of the components file?

BEGINRELEASENOTES

• Move create_segmentation to DDCore/include/DD4hep/detail/SegmentationsInterna.h to allow segmentation creation in other libraries
• Removed REGISTER_SEGMENTATION macro and DDSegmentation::SegmentationFactory class because they are obsolete. Use DECLARE_SEGMENTATION to create a plugin entry for segmentations.

ENDRELEASENOTES

[MarkusFrankATcernch]

DECLARE_SEGMENTATION creates the factory entry in the library.
The 'list_components' opens the library during make, reads all these entries
and writes the names into the components file.
If you do not have this entry, the factory mechanism is broken.

[andresailer]

Thanks for the confirmation!

[petricm]

If users are calling detail/SegmentationsInterna.h and this is necessary to create a segmentation then this header should not be in detail.

[andresailer]

Yeah, I kind of agree :)
I will try re-arranging so that the necessary pieces get pulled in via Segmentation.h or something like this?

[andresailer]

I re-arranged and removed some things in DDSegmentation that wasn't needed as far as I could tell.

I ran into some weird namespace issue, so I added DD4hep/Factories.h to all the Segmentation and replaced the REGISTER_SEGMENTATION macro with DECLARE_SEGMENTATION.
Removed some stuff for the obsolete REGISTER_SEGMENTATION
Removed the file with the now obsolete DECLARE_SEGMENTATION stuff

[andresailer]

Moving the DECLARE_SEGMENTATION to the individual segmentations leads these calls to be part of DDCore, which means any plugin linking against DDCore has these in their components file. Will bring back the ReadoutSegmentations.cpp file in plugin and leave the DECLARE_SEGMENTATION calls commented for people creating their own segmentations, in which case they probably create their own plugin in any case and it should be OK.

[vvolkl]

@andresailer so user code should also just replace REGISTER_SEGMENTATION with DECLARE_SEGMENTATION? Could you add a note to the Release Notes?