chore: Add tests for shapefile export

[gmaclennan]

mapeo.exportData({ format: 'shapefile' }) will export a Zip archive containing the files that make up a shapefile. This functionality does not currently have any tests. We should test and compare against a fixture and/or re-converting the shapefile back to GeoJSON to check it matches. We should manually test a fixture in QGIS to check it works. We should test with accented characters in both property names and values, and long property names (tag names) to check how Shapefile export handles that.

[hackergrrl]

• [ ] compare against a fixture
• [ ] re-convert the shapefile back to GeoJSON to check it matches
• [ ] manually test a fixture in QGIS to check it works
• [ ] test accented characters in both property names and values
• [ ] test long property names (tag names) to check how Shapefile export handles that