Rename testing stuff from "unit test" to "test" as appropriate

[DonJayamanne]

Three GitHub issues:

• Commands (labels for Commands in package.nls.json) (1)
• Upstream VSC Docs
• Configuration settings (prompt users to migrate, similar to how it was done for migration of launch.json settings, see how done today.) (2)
  • See src/client/application/diagnostics/checks/invalidDebuggerType.ts
• Messages displayed (1)

Change from:

• Unit Tests to Tests in labels
• unitTests to testing in settings.json

When in doubt check with @luabud