* Remove the local span and exit span register mechanism in Java agent scenario.
* Fix config, plugin, and document, as exit span is not required register anymore.
* Try to fix the test case expected data due to no register for exit span.
* Fix toolkit case.
* Remove exit span from plugin test framework document.
* Update protocol, FAQ, and CHANGELOG documents to highlight this change.
* Fix NPE when no entry span in the whole segment. Set endpoint to null in segment entity.
* Fix the snapshot and add inexistence operation name id.
* Fix several async cases.
* Fix undertow test case.
* Fix wrong error log name.
* Keep name consistent with 6.x concepts.
* Try to fix 3 async scenarios.
* Fix okhttp case.
* Fix Spring Async case.
* Fix another NPE
* Fix NPE when first span has no endpoint id when it is local or exit span.
* Still fill first operation name when no endpoint id.
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