Check for invalid polygonal geometry before fixing

[mdavis]

Some algorithms (including DouglasPeuckerSimplifier, VWSimplifier, Densifier) may produce invalid polygonal topology, and so include a cleaning step to ensure the result value is valid.

JTS has a PR to add a test to see if the result is actually invalid before running the potentially expensive cleaning process.

[mdavis]

JTS PR is ​656.

[mdavis]

Fixed by ​e6c6fa3.

[mdavis]

This produces a significant performance improvement in Densifier and DouglasPeuckerSimplifier.

Using a world dataset as a test, performance improves as shown below:

geosop -a world.wkt -t  densify .001

Ran 244 densify ops ( 366,951 vertices)  -- 24,765,297 usec    (GEOS 3.9.1dev)
Ran 244 densify ops ( 366,951 vertices)  -- 9,141,759 usec    (GEOS 3.10.0dev)

geosop -a world.wkt -t -r 10 simplifyDP .001

Ran 2,440 simplifyDP ops ( 366,951 vertices)  -- 9,296,279 usec    (GEOS 3.9.1dev)
Ran 2,440 simplifyDP ops ( 366,951 vertices)  -- 3,742,962 usec    (GEOS 3.10.0dev)