[code-reflection] Integrated: [hat] javadoc for TestDeviceType

[Juan Fumero]

Javadoc for `TestDeviceType` explaining how to use `DeviceType` and `DeviceSchema`.

-------------

Commit messages:
 - [hat] javadoc for TestDeviceType

Changes: https://git.openjdk.org/babylon/pull/683/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=683&range=00
  Stats: 40 lines in 1 file changed: 35 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/babylon/pull/683.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/683/head:pull/683

PR: https://git.openjdk.org/babylon/pull/683