RFR: 8287860: Revise usage of volatile in j.u.Locale

[liach]

On Mon, 6 Jun 2022 12:58:39 GMT, Сергей Цыпанов <duke at openjdk.java.net> wrote:

> - cached hash code of `Locale` and `Locale$LanguageRange` shouldn't be volatile, even in case of race in the worst case it is recalculated at most once per thread
> - `defaultLocale` field is read multiple times in `initDefault()`
> - `isoLanguages` is accessed multiple times in `getISOLanguages()`
> - `languageTag` is read twice in `toLanguageTag()`

src/java.base/share/classes/java/util/Locale.java line 2260:

> 2258:      * Calculated hashcode
> 2259:      */
> 2260:     private transient volatile int hashCodeValue;

We can additionally annotate such cache fields with `@Stable` so as to enable constant-folding optimizations from the hotspot JIT.

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PR: https://git.openjdk.java.net/jdk/pull/9041