Expose QgsGeos class to PyQGIS

[nyalldawson]

This class has lots of (very useful!) GEOS specific functionality which is not exposed through the base QgsGeometryEngine class.

Originally the intention was that the GEOS engine could be replaced by alternative engines at some stage, but that hasn't been used for the past decade and we're unlikely to see a pressing need for this in future.

[qgis-bot]

@nyalldawson

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[github-actions]

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