General thread attributes - Java's Thread.currentThread().getId() is deprecated

[arminru]

Thread.currentThread().getId() is deprecated since java 19. There is a Thread.currentThread().threadId() instead.

Originally posted by @johantiden in open-telemetry/opentelemetry-specification#789 (comment)

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This would need to be updated in https://github.com/open-telemetry/semantic-conventions/blob/main/docs/general/attributes.md#general-thread-attributes.

[johantiden]

To reiterate:
Thread.currentThread().getId() has been deprecated in favor of Thread.currentThread().threadId(), which is more secure since it can't be overridden.
https://bugs.openjdk.org/browse/JDK-8017617?page=com.atlassian.jira.plugin.system.issuetabpanels%3Aall-tabpanel

We should change the example docs to reflect the latest Java LTS version.