RFR: 8340073: Support "%z" time zone abbreviation format in TZ files

[Naoto Sato]

Yet another preparation for upgrading the time zone data to 2024b, which introduced a new abbreviation format "%z". The update includes:
...
      The main source files' time zone abbreviations now use %z,
      supported by zic since release 2015f and used in vanguard form
      since release 2022b. For example, America/Sao_Paulo now contains
      the zone continuation line "-3:00 Brazil %z", which is less error
      prone than the old "-3:00 Brazil -03/-02". This does not change
      the represented data: the generated TZif files are unchanged.
      Rearguard form still avoids %z, to support obsolescent parsers.
...

Also fixed the logic to retrieve the linked tz name that is chaining.

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Commit messages:
 - initial commit

Changes: https://git.openjdk.org/jdk/pull/20979/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20979&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340073
  Stats: 20 lines in 2 files changed: 12 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/20979.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20979/head:pull/20979

PR: https://git.openjdk.org/jdk/pull/20979