Store `cmprefimpl` strings in a separate file

[peterstace]

Currently, the input strings for the cmprefimpl tests are scraped from the simplefeatures codebase. The intention is that the unit tests in the codebase contain a lot of WKT literals, which are perfect inputs for the cmprefimpl tests.

This approach has the downside that the addition of new unit tests can sometimes cause the cmprefimpl tests to fail. Any additional unit tests (with novel inputs) can create additional cmprefimpl test cases, which may fail.

It would be nice if the cmprefimpl inputs were decoupled from the unit tests. One way to do this could be to:

• Store the inputs to cmprefimpl in a text file (under version control).
• Create a utility to scrape the codebase to populate the text file. This utility would be run manually.
• The utility might need blacklisting functionality.