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ARROW-7495: [Java] Remove "empty" concept from ArrowBuf, replace with custom referencemanager (#6433)

* ARROW-7495: [Java] Remove "empty" concept from ArrowBuf, replace with custom referencemanager

* fix orc

* add ut

* add static method to create empty ArrowBuf

* resolve conflicts

* add tests to test empty ArrowBuf behavior

* fix style

* add more test cases

* rebase