Flink: backport PR #7978. switch to FileScanTaskParser for JSON serialization of IcebergSourceSplit

[stevenzwu]

it is a clean back port.

confirmed git diff

➜  iceberg git:(backport-7978) ✗ git diff --no-index  flink/v1.15/flink/src/main/java/org/apache/iceberg/flink/source  flink/v1.17/flink/src/main/java/org/apache/iceberg/flink/source
➜  iceberg git:(backport-7978) ✗ git diff --no-index  flink/v1.16/flink/src/main/java/org/apache/iceberg/flink/source  flink/v1.17/flink/src/main/java/org/apache/iceberg/flink/source

test folder has some diff related to assertj change, not related to this change

➜  iceberg git:(backport-7978) ✗ git diff --no-index  flink/v1.15/flink/src/test/java/org/apache/iceberg/flink/source  flink/v1.17/flink/src/test/java/org/apache/iceberg/flink/source
➜  iceberg git:(backport-7978) ✗ git diff --no-index  flink/v1.16/flink/src/test/java/org/apache/iceberg/flink/source  flink/v1.17/flink/src/test/java/org/apache/iceberg/flink/source

[ConeyLiu]

+1 for backport

[stevenzwu]

thanks @pvary and @ConeyLiu for reviews