purl-next: Extend the PURL tests for registered PURL types

[pombredanne]

We need to extend the PURL JSON test suite for each type. This means migrating existing tests, as well as integrating examples and creating new tests using the new JSON schema for tests.

[pombredanne]

This has been merged with:

• Refine Purl type schema package-url/purl-spec#514

Use the new schema at:

• https://github.com/package-url/purl-spec/blob/main/schemas/purl-test.schema.json

We now have a comprehensive test suite for all the registered PURL types in:

• https://github.com/package-url/purl-spec/tree/main/tests

The full list is now in this JSON:

As an example here are the tests for npm:

• https://github.com/package-url/purl-spec/tree/main/tests/types/npm-test.json

The test suite has also been significantly expanded.