[FEAT] Consider using the originally planned Loop marker

[tbouffard]

Due to an issue in the proposed loop svg transformation into mxgraph code (see https://github.com/process-analytics/bpmn-visualization-js/issues/303#issuecomment-669083057 and #464), we currently (0.1.7-dev) don't use the proposed icon. As we agreed to use this one, give it another chance

Decision

Decided on 2024-04-04 (see #2724)

• reduce width and keep the existing design
• this also require to introduce a mechanism to enforce the marker width: #465

[tbouffard]

Be aware of this prototype which doesn't change the loop marker: https://github.com/process-analytics/bpmn-visualization-js/pull/2724#issuecomment-1997932820