ST_LocateBetween[Elevations]: support POLYGON

Output may be invalid for non-convex, area is preserved.

References #4155
Closes https://github.com/postgis/postgis/pull/319



git-svn-id: http://svn.osgeo.org/postgis/trunk@16952 b70326c6-7e19-0410-871a-916f4a2858ee
1 job for svn-trunk in 34 minutes and 14 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #112899991
test

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