KAFKA-19562: Replace hand-written AbortedTxn with generated protocol

[mingyen066]

Replace the manually maintained AbortedTxn class with a generated
protocol message defined in AbortedTxn.json.

Also simplifies TransactionIndex buffer management since the generated
class copies field values at construction time instead of holding a
buffer reference.

Reviewers: Chia-Ping Tsai chia7712@gmail.com

[chia7712]

@mingyen066 please handle the conflicts

[chia7712]

Execution failed for task ':tools:compileTestJava'.
> Compilation failed; see the compiler output below.
  /home/chia7712/project/kafka/tools/src/test/java/org/apache/kafka/tools/DumpLogSegmentsTest.java:88: error: cannot find symbol
  import org.apache.kafka.storage.internals.log.AbortedTxn;
                                               ^
    symbol:   class AbortedTxn
    location: package org.apache.kafka.storage.internals.log
  /home/chia7712/project/kafka/tools/src/test/java/org/apache/kafka/tools/DumpLogSegmentsTest.java:1489: error: cannot find symbol
              index.append(new AbortedTxn(1L, 0, 10, 11));
                               ^
    symbol:   class AbortedTxn
    location: class DumpLogSegmentsTest
  /home/chia7712/project/kafka/tools/src/test/java/org/apache/kafka/tools/DumpLogSegmentsTest.java:1490: error: cannot find symbol
              index.append(new AbortedTxn(2L, 15, 25, 26));
                               ^
    symbol:   class AbortedTxn
    location: class DumpLogSegmentsTest
  3 errors

* Try:
> Check your code and dependencies to fix the compilation error(s)