[jdk24u] RFR: 8347424: Fix and rewrite sun/security/x509/DNSName/LeadingPeriod.java test

[Aleksey Shipilev]

Backporting for completeness against 17u and 21u.

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Commit messages:
 - Backport a6be9076351b591cbc0860b1ba8f3c56319f4ffe

Changes: https://git.openjdk.org/jdk24u/pull/23/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk24u&pr=23&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347424
  Stats: 63 lines in 1 file changed: 1 ins; 44 del; 18 mod
  Patch: https://git.openjdk.org/jdk24u/pull/23.diff
  Fetch: git fetch https://git.openjdk.org/jdk24u.git pull/23/head:pull/23

PR: https://git.openjdk.org/jdk24u/pull/23