workspace/tests request does not return swift-testing tests

[adam-fowler]

Also symbol information is probably not enough information for each test. The following additional information would be useful

• source: Did test come from xctest or swift-testing
• label: swift-testing tests can have a label, displaying this in the UI would be good.

swift-testing tests can have a whole bunch more data attached to them but I'm not sure at this time if it is needed. It can always be added at a later date.

[ahoppen]

Tracked in Apple’s issue tracker as rdar://119191037