Add force_polygon_cw and force_polygon_ccw expression functions

[nyalldawson]

These are recommended for use instead of the existing force_rhr function, due to the variability in definition of the "right hand rule" between different software applications. Using an explicit force_polygon_cw/ccw function removes user confusion when the results vary between different applications.

(Note that this matches PostGIS' recommendations now: see https://postgis.net/docs/ST_ForceRHR.html )

I'd like to backport this to 3.22 too.

[github-actions]

@nyalldawson
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[github-actions]

@nyalldawson
A documentation ticket has been opened at qgis/QGIS-Documentation#7010
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!