Render S-group abbreviations in PNG and SVG

**Background**

Ketcher displays the standard S-group abbreviation outside the closing bracket, at its lower-right side.
Supporting Ketcher issue: https://github.com/epam/ketcher/issues/10457

**Requirements**

1. Display the abbreviation outside the closing bracket, at its lower-right side:
SRU polymer — polymer label, n by default
Multiple group — repeat count
Copolymer without a subtype — co
Copolymer, alternating — alt
Copolymer, block — blk
Copolymer, random — ran
Superatom — superatom name
Data — no abbreviation

2. Render brackets and the repeat pattern for Copolymer in the same way as for SRU polymer.

No source files, tests, or entry points are named. Start by tracing the PNG and SVG rendering paths for S-groups, then review the supporting Ketcher issue #10457. Done means the listed abbreviations, bracket placement, and copolymer repeat pattern render correctly, while Data has no abbreviation.

Written by the indexing model from the issue text.