<i18n dev> RFR: 8372460: Use EnumMap instead of HashMap for DateTimeFormatter parsing to improve performance

[Shaojin Wen]

This PR optimizes the parsing performance of DateTimeFormatter by replacing HashMap with EnumMap in scenarios where the keys are exclusively ChronoField enum values.

When parsing date/time strings, DateTimeFormatter creates HashMaps to store intermediate parsed values. HashMap has more overhead for operations compared to specialized map implementations.

Since ChronoField is an enum and all keys in these maps are ChronoField instances, we can use EnumMap instead, which provides better performance for enum keys due to its optimized internal structure.

Parsing scenarios show improvements from 12% to 95%

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Commit messages:
 - bug fix, form @liach
 - use EnumMap
 - add benchmark

Changes: https://git.openjdk.org/jdk/pull/28471/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28471&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372460
  Stats: 153 lines in 5 files changed: 149 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/28471.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28471/head:pull/28471

PR: https://git.openjdk.org/jdk/pull/28471