<i18n dev> RFR: 8283781: Avoid allocating unused lastRulesCaches

[Claes Redestad]

This address a minor inefficiency in that the `ZoneRules` of any `ZoneOffset` (and some `ZoneRegion`s) allocate `lastRulesCache` unnecessarily.

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Commit messages:
 - Merge branch 'master' into lastRulesCache
 - Avoid allocating unused lastRulesCaches

Changes: https://git.openjdk.java.net/jdk/pull/7990/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7990&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283781
  Stats: 16 lines in 1 file changed: 9 ins; 2 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7990.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7990/head:pull/7990

PR: https://git.openjdk.java.net/jdk/pull/7990