[FEAT] Provide a way to configure the defaults of the BPMN renderer

[tbouffard]

Is your feature request related to a problem? Please describe.

I would like to be able to change the defaults at bpmn-visualization initialization. At least for settings shared by all elements:

• fill color
• stroke color
• font: family, color, size

Describe the solution you'd like

Currently, examples show hacks to modify the defaults. They involve changing internal values or extending the library.
I would like to be able to do it without changing the lib internals.

[UPDATE 2023-07-13]
For more details, see #2659 (comment)

• we will propose to update the style defaults using mxGraph global styles. A dedicated API will be introduced with something similar to what is describe in [FEAT] General improvements for default styles management #2471 (dedicated styles related methods)
• the overlay defaults will be configurable at the lib initialization by using options.
• some rendering options can no longer be updated after this change. They are covering rare use cases. We will support them back if users request it

Meta tasks

• Update the examples: for defaults non related to the overlays, stop using StyleDefaut and use mxGraph global styles instead refactor(theme): use global style instead of StyleDefault bpmn-visualization-examples#519
• Deprecate StyleDefaut to notice user that it is going to be removed from the public API (it was experimental) or at least warn user in the release notes.
• Introduce default overlay settings in the RenderOptions (see [FEAT] Define the options that will be used to configure the Renderer #2659) and
• Update the examples to use the new RendererOptions for overlay defaults
• Make StyleDefautinternal (breaking changes).

Additional context

Available examples in v0.23.3:

• custom colors
• custom fonts

These examples use an hack that update the values defined in StyleDefault. The changes are global so they have side effects. It is also not very friendly to use this hack.

Initial proposal for a way to pass defaults

This could be done with something like (non exhaustive, just for illustration)

new BpmnVisualization({
  renderer: {
    defaults: {
      fillColor: 'pink';
      font: {
        color: 'orange';
        family: 'Georgia, serif';
        size: 13;
      };
      strokeColor: 'red';
    }
  }
})

⚠️ Important ⚠️:

• the name of the properties must be consistent with the properties we use to style Overlays and what we plan in [FEAT] Configure programatically the style of a Shape/Edge #1030 and [REFACTOR] Mutualize the programatic styling APIs of Shapes/Edges with that of Overlays #2457.
• the choice about the structure of the renderer options will be taken through [FEAT] Define the options that will be used to configure the Renderer #2659