Add mechanism to use standard test geometries in cunit suite

[dbaston]

It's currently a bit of a pain to add cunit tests to cover all of the available geometry types, especially when you think of all the different ways to get an EMPTY. I think it would be worthwhile to create a standard list of test geometries that can be pulled in to any individual test as desired.

Maybe this would be as simple as a text file of WKT entries with an ID for each; some helper functions would then let you:

• bring in an individual geometry by ID
• bring in an array of all test available geometries meeting certain filters (3d yes/no, measures yes/no, curves yes/no, empty yes/no, etc).

[komzpa]

Fuzzers have a concept of "corpus", a directory of input files that exercise a bunch of code paths. libfuzzer has a mode to minimize such a directory, add a new sample and go look for ones that cover some more lines. Such directory can be shared with cunit tests too.