kvserver: ClearRange optimization does not remove separated intents

[erikgrinaker]

ClearRange normally uses Writer.ClearMVCCRangeAndIntents to remove the range, but has an optimization for small ranges where it instead removes keys directly:

cockroach/pkg/kv/kvserver/batcheval/cmd_clear_range.go

Lines 84 to 109 in b7fb524

	// If the total size of data to be cleared is less than
	// clearRangeBytesThreshold, clear the individual values manually,
	// instead of using a range tombstone (inefficient for small ranges).
	if total := statsDelta.Total(); total < ClearRangeBytesThreshold {
	log.VEventf(ctx, 2, "delta=%d < threshold=%d; using non-range clear", total, ClearRangeBytesThreshold)
	iter := readWriter.NewEngineIterator(storage.IterOptions{UpperBound: to})
	valid, err := iter.SeekEngineKeyGE(storage.EngineKey{Key: from})
	for ; valid; valid, err = iter.NextEngineKey() {
	var k storage.EngineKey
	if k, err = iter.UnsafeEngineKey(); err != nil {
	break
	}
	if err = readWriter.ClearEngineKey(k); err != nil {
	return result.Result{}, err
	}
	}
	iter.Close()
	if err != nil {
	return result.Result{}, err
	}
	return pd, nil
	}
	if err := readWriter.ClearMVCCRangeAndIntents(from, to); err != nil {
	return result.Result{}, err
	}

However, when clusterversion.SeparatedIntents is enabled, this will only remove the key but not its intent (which is stored in a separate lock table). This can cause subsequent Engine operations to error because of the unexpected intent, as seen e.g. in TestTxnClearRangeIntents in #61544.

This is related to #46764, in that clearing intents may in itself be considered a bug since it can abort an implicitly committed transaction.