[crac] RFR: Improve C/R exception printout [v2]

[Radim Vansa]

> Some users might get confused by the inner exceptions reported during C/R as *suppressed* exceptions. This PR changes the printout to make it look as if the exception had multiple causes. For example the DryRunTest will report this:
> 
> jdk.crac.CheckpointException: Failed with 2 inner exceptions
> Cause 1/2: java.lang.RuntimeException: should not pass
> 	at DryRunTest$CRResource.beforeCheckpoint(DryRunTest.java:47)
> 	at java.base/jdk.crac.impl.AbstractContext.invokeBeforeCheckpoint(AbstractContext.java:44)
> 	... (redacted)
> Cause 2/2: jdk.crac.impl.CheckpointOpenFileException: /tmp/jtreg-DryRunTest6956725915963168340.tmp
> 	at java.base/jdk.internal.crac.JDKFileResource.lambda$beforeCheckpoint$1(JDKFileResource.java:89)
> 	at java.base/jdk.crac.Core.checkpointRestore1(Core.java:174)
>         ... (redacted)

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

  Replace suppressed exceptions with nested ones

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

Changes:
  - all: https://git.openjdk.org/crac/pull/145/files
  - new: https://git.openjdk.org/crac/pull/145/files/474b1638..5f011c94

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=crac&pr=145&range=01
 - incr: https://webrevs.openjdk.org/?repo=crac&pr=145&range=00-01

  Stats: 274 lines in 19 files changed: 142 ins; 62 del; 70 mod
  Patch: https://git.openjdk.org/crac/pull/145.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/145/head:pull/145

PR: https://git.openjdk.org/crac/pull/145