[code-reflection] RFR: [hat] Assert moved to hat.test.exceptions package

[Juan Fumero]

HATAsserts is moved to exceptions package within the testing framework.

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Commit messages:
 - [hat] Assert moved to hat.test.exceptions package

Changes: https://git.openjdk.org/babylon/pull/744/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=744&range=00
  Stats: 10 lines in 2 files changed: 1 ins; 9 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/744.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/744/head:pull/744

PR: https://git.openjdk.org/babylon/pull/744