Refactor test resources to separate JSON Schema Test Suite files from project specific files

[fdutton]

I propose moving the specification files from JSON Schema Test Suite to src/test/suite. This would provide the following benefits:

• Makes merging updates from that project into this one easier as it reduces the chance of removing or overwriting this project's files
• Makes it easier to see exactly what changed in the specification thus making it easier to see what functional changes are required to conform (e.g., content.json moved from draft2019-09/optional to draft2019-09 and draft2019-09/optional/zeroTerminatedFloats.json was removed)
• Enables the opportunity to populate src/test/suite by linking to that project thus eliminating the need to manually merge its changes into this project (it is also possible for Maven to download and unpack a specific version of the source code)
• Enables more complicated processing of specification files. JSON Schema Test Suite has informed validators to expect specification files to appear at the root of the tests folder. The validators are now expected to extract $schema from the specification file rather than using the folder name (e.g., tests/draft2019-09)

This change depends on #690 being accepted.

[stevehu]

@fdutton This is a fantastic idea. Maintaining the Test Suite is time-consuming as the target changes all the time. Thanks.