RFR: 8311546: Certificate name constraints improperly validated with leading period

[Ben Perez]

Updated the `constrains` method in `DNSName.java` to accept certificates with a leading period.

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Commit messages:
 - removed tabs
 - replaced tabs with spaces
 - Merge branch 'openjdk:master' into JDK-8311546
 - Changed documentation for LeadingPeriod test
 - Removed unnecessary doc
 - removed unnecessary files related to cert generation
 - Added test for checking certs with leading period
 - Added check for leading '.' in DNS name

Changes: https://git.openjdk.org/jdk/pull/16295/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16295&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311546
  Stats: 316 lines in 8 files changed: 314 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16295.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16295/head:pull/16295

PR: https://git.openjdk.org/jdk/pull/16295