RFR: 8302983: ZoneRulesProvider.registerProvider() twice will remove provider [v3]

[Madjosz]

> Fixes JDK-8302983 (and duplicate JDK-8302898)

Madjosz has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  apply review comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12690/files
  - new: https://git.openjdk.org/jdk/pull/12690/files/0c7e5889..1bcf7bd8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12690&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12690&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12690.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12690/head:pull/12690

PR: https://git.openjdk.org/jdk/pull/12690