ICU-22761 Optimize get value of LocaleObjectCache

[imurluck]

When invoking get(K key) method of LocaleObjectCache, it may be blocked for a long time, looping in lines 45 and 53, because after the referent of SoftReference is set to NULL, it may take a long time to add SoftReference to its ReferenceQueue if GC is slowly.

For example, in the Concurrent Copying GC in Android Art virtual machine, the referent in SoftReference is set to null during the copying phase, while the SoftReference is added to its ReferenceQueue in the ReferenceQueueDaemon thread after GC, which experiences a long time in between

In fact, we have found many examples of blocking for more than 10s on some Android devices

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22761
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

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[imurluck]

https://github.com/frohoff/jdk8u-jdk/blob/master/src/share/classes/sun/util/locale/LocaleObjectCache.java

There is no while loop in the implementation of jdk8