[jdk21u-dev] RFR: 8339644: Improve parsing of Day/Month in tzdata rules

[Goetz Lindenmaier]

I backport this for parity with 21.0.6-oracle.

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Commit messages:
 - Backport 86a2f9c7dcb6585cabf03c0940511d11560e85b7

Changes: https://git.openjdk.org/jdk21u-dev/pull/979/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=979&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339644
  Stats: 83 lines in 3 files changed: 23 ins; 26 del; 34 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/979.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/979/head:pull/979

PR: https://git.openjdk.org/jdk21u-dev/pull/979