[jdk21u] RFR: 8316415: Parallelize sun/security/rsa/SignedObjectChain.java subtests

[Aleksey Shipilev]

Clean backport to improve test performance.

Additional testing:
 - [x] MacOS AArch64 server fastdebug, C1, test passes and time improves

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Commit messages:
 - Backport 59847926b63860704bcf2967660628eaede8ee36

Changes: https://git.openjdk.org/jdk21u/pull/395/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=395&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316415
  Stats: 7 lines in 1 file changed: 2 ins; 2 del; 3 mod
  Patch: https://git.openjdk.org/jdk21u/pull/395.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/395/head:pull/395

PR: https://git.openjdk.org/jdk21u/pull/395