[FEAT] Add a new API to reset the modified style of given elements via APIs

[csouchet]

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

#1030 lets change the style of an element. Some use cases requires to reset the whole modifications applied to the element

• highlight on mouse hover
• switching from a data representation to another: the 2 representations don't need to customize the same style properties and may not know each other, so a reset should occur prior switching.

Describe the solution you'd like

Introduce a new API method that allows you to reset the style of an element or a list of elements as they were defined before any modification.

In the same class as for the "Update Style" API (see #1030)

resetStyle(bpmnElementIds?: string | string[]): void

Calling the method without argument will reset the style on all elements.
This signature matches the removeAllCssClasses signature (#2576) and the removeAllOverlays signature (#2577).

Additional Context

The implementation will depend on how mxGraph stores the styles in the model.

Prerequisites:

• How does mxGraph store styles and compute them?
• How to manipulate the style? State object or model object?
• How to make style changes?
• How can we reset to the initial style?

Experimentation done in the POC #2539

• Introduce a custom UndoManager to store the first style change of each cell to store the default style of them, at each call of updateStyle if is not stored.

• It is deleted on each calling of resetStyle.

• https://github.com/process-analytics/bpmn-visualization-js/pull/2539/files#diff-8d1211cbbc8caf5463e0a05fb2c4469e62dd5a966a1f4e0225474257cd3a05ef

• https://github.com/process-analytics/bpmn-visualization-js/pull/2539/files#diff-5a78c9398ffd553bf04f09484ed9434cae1da4dcce9389b73930257e8e6558a9

• https://github.com/process-analytics/bpmn-visualization-js/pull/2539/files#diff-6f664385f002a6733b3bf55ab1de337505fcf1665216f8d7d81b055eb413f555R301

• https://github.com/process-analytics/bpmn-visualization-js/pull/2539/files#diff-6f664385f002a6733b3bf55ab1de337505fcf1665216f8d7d81b055eb413f555R321

• https://github.com/process-analytics/bpmn-visualization-js/pull/2539/files#diff-6f664385f002a6733b3bf55ab1de337505fcf1665216f8d7d81b055eb413f555R335

• https://github.com/process-analytics/bpmn-visualization-js/pull/2539/files#diff-6f664385f002a6733b3bf55ab1de337505fcf1665216f8d7d81b055eb413f555R473

Alternative

Use the same logic as in #2574
Set all properties to null in the mxGraph style.
As explained in #2574, this will cause side effects for the font if the BPMN diagram defined a LabelStyle for the BPMN element whose style is updated (could work if label style is ignored, see #2468).
In addition, this won't let support the reset on all elements: we wouldn't register the update elements so we would have to apply the reset to all elements of the diagram instead on only these that have actually been updated.