[Enhancement] add "add-polygon" icon to replace existing "add-polygone"

[ilhan007]

Feature Request

The add-polygone icon name has typo in it - it should have been add-polygon. This is already reported to the SAP Design team. Meanwhile let's create an icon with the correct name add-polygon (with the same path as add-polygone) and keep the old one for compatibility.
The add-polygone is already listed in the 2.0 braking change list and will be removed in future.

Expected Behavior

• Add new icon add-polygon (a copy of add-polygone ) to the SAP Business Suite Icon collection.
• Replace the usage of add-polygone in the project with add-polygon

Additional info

This is already reflected in the woff-to-svg tool - the SAP BS Icons charcode list is updated and add-polygon is included and new note is added to README.md to describe this special case, that should be taken care when updating the SAP BS Icons charcode list.

Context

• UI5 Web Components version: {...}
• OS/Platform: {...}
• Browser: {...}
• Affected component: {...}