Use EnumMap instead of HashMap for DateTimeFormatter parsing to improve performance

[wenshao]

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%.
To better express my ideas, I submitted a draft PR: https://github.com/openjdk/jdk/pull/28471 <https://github.com/openjdk/jdk/pull/28471 > , and I hope you can give me feedback.
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Shaojin Wen
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