8372460: Use EnumMap instead of HashMap for DateTimeFormatter parsing to improve performance

[RogerRiggs]

Refactor java.time.format.Parsed to use an EnumMap<ChronoField,Long> by default and upgrade to a HashMap if any of the fields are not ChronoFields.
In the java.time implementation all of the fields used are ChronoField.
Unless the application introduces a custom TemporalField there is no additional overhead.

This an alternative to PR #28471

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Issue

• JDK-8372460: Use EnumMap instead of HashMap for DateTimeFormatter parsing to improve performance (Enhancement - P4)

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[liach]

This map is passed to TemporalField::resolve, so this approach is risky.

[liach]

Suggested change

	private Map<TemporalField, Long> initFieldValuesMap() {
	private static Map<TemporalField, Long> initFieldValuesMap() {

Let's make this static to be early-construction safe.

[liach]

Suggested change

	Map<TemporalField, Long> nmap = new HashMap<>(fieldValues.size() + 1);
	Map<TemporalField, Long> nmap = HashMap.newHashMap(fieldValues.size() + 1);

We might still anticipate more elements to be put into the map, so a better alternative might be just new HashMap<>(fieldValues)?