Support Any Polymer, Mer, Generic, and Monomer S-groups

[Mihajlovic-Marko]

Background

Ketcher will allow users to create Any Polymer, Mer, Generic, and Monomer S-groups. Indigo should preserve these types and their properties when structures are loaded, saved, and converted.
Supporting Ketcher issue: epam/ketcher#10665

Requirements

Indigo should support conversion between KET and MOL V2000 and V3000 formats and their variants, CDX, and CDXML.

KET

KET should represent the following as separate S-group types:
Any Polymer
Mer
Generic
Monomer
The S-group type, included atoms, and repeat pattern should be preserved.

MOL V2000

Support:
ANY — Any Polymer
MER — Mer
GEN — Generic
MON — Monomer
The repeat pattern should be read from and written to M SCN.

MOL V3000

Support:
ANY — Any Polymer
GEN — Generic
MON — Monomer
The repeat pattern should be read from and written to CONNECT.

CDX and CDXML

Any Polymer, Mer, Generic, Monomer, and repeat pattern information should be converted to and from the corresponding KET representation.

Indigo should correctly render all functions in PNG and SVG.