[jdk8u-dev] RFR: 8186143: keytool -ext option doesn't accept wildcards for DNS subject alternative names

[Alexey Bakhtin]

I backport this for parity with Oracle 8u351
Almost clean backport except for DNSName.java: 
small manual merge in the constructor caused by the absence of "JDK-8215281: Use String.isEmpty() when applicable in java.base"

All sun/security/x509 and sun/security/tools/keytool JTREG tests passed

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Commit messages:
 - Backport 0c9f8e472f1d452e97b3cbd50b9e5d700fffcd15

Changes: https://git.openjdk.org/jdk8u-dev/pull/629/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=629&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8186143
  Stats: 109 lines in 3 files changed: 96 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/629.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/629/head:pull/629

PR: https://git.openjdk.org/jdk8u-dev/pull/629