processor,sink(cdc): let sink report resolved ts and do not skip buffer sink flush (#3540)

[ti-chi-bot]

This is an automated cherry-pick of #3540

What problem does this PR solve?

Revert #3029 and #2617 temporary for resolving #3503.

Cc https://github.com/pingcap/ticdc/issues/3545

Check List

Tests

• Integration test

See #3503

Release note

None

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[overvenus]

/merge

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This pull request has been accepted and is ready to merge.

Commit hash: d3058be

[overvenus]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ef1d578

[overvenus]

/run-integration-test

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@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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