Summary:
This revision adds support for filtering aborted subtransactions (rolled-back savepoints) in CDC streaming.

Previously, the apply path (ProcessApply) correctly skipped intents from aborted sub-transactions, but the CDC streaming path (GetIntentsBatchForCDC) did not, causing CDC consumers to receive data from rolled-back savepoints that should have been discarded.

This change propagates the aborted sub-transaction set through the CDC call chain (cdcsdk_producer.cc -> tablet.cc -> docdb.cc) and updates GetIntentsBatchForCDC to skip intents from aborted sub-transactions, aligning its behaviour with the apply path.
Jira: DB-11714

Test Plan: ./yb_build.sh --cxx-test cdcsdk_consumption_consistent_changes-test --gtest_filter CDCSDKConsumptionConsistentChangesTest.TestCDCWithSavePoint

Reviewers: sumukh.phalgaonkar, devansh.saxena, skumar, asrinivasan

Reviewed By: skumar

Subscribers: svc_phabricator, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D47790