GeoServer <sld:VendorOptions name="graphic-margin" /> handling is unstable

[sebastianfrey]

Bug

Describe the bug
The in #971 introduced support for GeoServer <sld:VendorOptions name="graphic-margin" /> tags, does not handle all supported format definitions of the graphic-margin property.

Currently the parser expects multiple margins to be separated by comma. As stated in this GeoServer guide, multiple margins can be separated by space.

To Reproduce
Steps to reproduce the behavior:
1.Use https://github.com/geostyler/geostyler-sld-parser/blob/main/data/slds/geoserver/pattern_polygon.sld

1. Change all commas for <sld:VendorOptions name="graphic-margin" /> to spaces
2. Symbolizer#graphicFillPadding is an array of NaN.

Expected behavior
<sld:VendorOptions name="graphic-margin" /> tags with multiple margins separated by space should be supported.

Screenshots

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Additional context

If desired I am happy, to provide a PR to fix this bug.