<i18n dev> RFR: 8320919: Clarify Locale related system properties

[Naoto Sato]

This is a doc change to clarify what the `Default Locale` is, and how it is established during the system startup using the system properties. Those locale-related system properties have existed since the early days of Java, but have never been publicly documented before. It is also the intention of this PR to clarify those system properties and how they are overridden. A corresponding CSR has been drafted.

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

Commit messages:
 - 6th draft
 - 5th draft
 - 4th draft
 - 3rd draft
 - 2nd draft
 - initial commt

Changes: https://git.openjdk.org/jdk/pull/17065/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17065&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320919
  Stats: 81 lines in 1 file changed: 71 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/17065.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17065/head:pull/17065

PR: https://git.openjdk.org/jdk/pull/17065