[BUG] Conditional sequence flow marker sometimes overlapped by the edge line

[tbouffard]

Describe the bug
Seen in [email protected] but existed before.
When zooming on the flows.sequence.kinds.and.complex.paths.bpmn non regression diagram, depending on the scale, the line overlaps the diamond.

This issue is always visible with the adonis-np-8_0-miwg-A.2.1-export.bpmn (from miwg-test-suite, also available in the xml-parsing test diagrams folder)

To Reproduce
This issue is reproducible at least on Windows and Ubuntu, with Firefox and Chrome, and seems related to the mxgraph integration (see below).

Additional context

Notes:

• This may be an issue in the scaling computation done by mxGraph (there is never issue on panning). mxGraph 4.1.1 introduces changes/fixes in this area (to be checked as part of [INFRA] Bump mxgraph to 4.2.2 #919).
• When disabling 'orthogonal segments' ([BUG] Message/Sequence flow segments shouldn't always be orthogonal #295), this appears at any zoom level, see [FIX] do not force usage orthogonal edge segments #351 (comment).

As a workaround, we may fill the the diamond with the default fill color (white) as it is also suggested for message flow start marker (#995). The current style configuration explicitly set no fill color

      SequenceFlowKind.CONDITIONAL_FROM_ACTIVITY,
      (style: StyleMap) => {
        style[mxConstants.STYLE_STARTARROW] = mxConstants.ARROW_DIAMOND_THIN;
        style[mxConstants.STYLE_STARTSIZE] = 18;
        style[mxConstants.STYLE_STARTFILL] = false;
      },

Notice that we should 1st try to understand if this is a scaling computation issue, as it may impact other part of the BPMN rendering.

[tbouffard]

This may be the same root cause as #994. See #994 (comment)
--> confirmed that this is the root cause (scaling issue, some points are removed)