## What changes were proposed in this pull request?
As the user uses Kafka transactions to write data, the offsets in Kafka will be non-consecutive. It will contains some transaction (commit or abort) markers. In addition, if the consumer's `isolation.level` is `read_committed`, `poll` will not return aborted messages either. Hence, we will see non-consecutive offsets in the date returned by `poll`. However, as `seekToEnd` may move the offset point to these missing offsets, there are 4 possible corner cases we need to support:
- The whole batch contains no data messages
- The first offset in a batch is not a committed data message
- The last offset in a batch is not a committed data message
- There is a gap in the middle of a batch
They are all covered by the new unit tests.
## How was this patch tested?
The new unit tests.
Closes#22042 from zsxwing/kafka-transaction-read.
Authored-by: Shixiong Zhu <zsxwing@gmail.com>
Signed-off-by: Shixiong Zhu <zsxwing@gmail.com>
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