[crac] RFR: Use special class for exception aggregates [v6]

[Radim Vansa]

> Extracted non-essential changes from other PR.

Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:

  Dropped empty files (merge artifact)

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Changes:
  - all: https://git.openjdk.org/crac/pull/64/files
  - new: https://git.openjdk.org/crac/pull/64/files/82582932..128b64a3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=64&range=05
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=64&range=04-05

  Stats: 0 lines in 2 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/crac/pull/64.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/64/head:pull/64

PR: https://git.openjdk.org/crac/pull/64