Retry on BatchCoprocessor request may fail randomly

[windtalker]

Bug Report

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The root cause is when retry a batch coprocessor request, we just collect the key ranges in the failed batch coprocessor request:

tidb/store/copr/batch_coprocessor.go

Lines 1094 to 1123 in 1837efe

	func (b *batchCopIterator) retryBatchCopTask(ctx context.Context, bo *backoff.Backoffer, batchTask *batchCopTask) ([]*batchCopTask, error) {
	if batchTask.regionInfos != nil {
	var ranges []kv.KeyRange
	for _, ri := range batchTask.regionInfos {
	ri.Ranges.Do(func(ran *kv.KeyRange) {
	ranges = append(ranges, *ran)
	})
	}
	ret, err := buildBatchCopTasksForNonPartitionedTable(ctx, bo, b.store, NewKeyRanges(ranges), b.req.StoreType, false, 0, false, 0, tiflashcompute.DispatchPolicyInvalid)
	return ret, err
	}
	// Retry Partition Table Scan
	keyRanges := make([]*KeyRanges, 0, len(batchTask.PartitionTableRegions))
	pid := make([]int64, 0, len(batchTask.PartitionTableRegions))
	for _, trs := range batchTask.PartitionTableRegions {
	pid = append(pid, trs.PhysicalTableId)
	ranges := make([]kv.KeyRange, 0, len(trs.Regions))
	for _, ri := range trs.Regions {
	for _, ran := range ri.Ranges {
	ranges = append(ranges, kv.KeyRange{
	StartKey: ran.Start,
	EndKey: ran.End,
	})
	}
	}
	keyRanges = append(keyRanges, NewKeyRanges(ranges))
	}
	ret, err := buildBatchCopTasksForPartitionedTable(ctx, bo, b.store, keyRanges, b.req.StoreType, false, 0, false, 0, pid, tiflashcompute.DispatchPolicyInvalid)
	return ret, err
	}

But, for buildBatchCopTasksForNonPartitionedTable and buildBatchCopTasksForPartitionedTable, it actually assumes that the input key ranges is sorted. So an unsorted input may cause wrong result in SplitKeyRangesByLocations, and TiFlash may throw errors like
Error 1105 (HY000): [FLASH:Coprocessor:BadRequest] Income key ranges is illegal for region: 326: (while doing learner read for table, logical table_id: 2593)

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