Support keepOrder = true for partition table in BatchPointGetExec

[Defined2014]

Enhancement

To support keepOrder, we should support sort handles from different partition in func (e *BatchPointGetExec) initialize(ctx context.Context), like

tidb/executor/batch_point_get.go

Lines 256 to 263 in 0e068ed

	if e.keepOrder {
	slices.SortFunc(toFetchIndexKeys, func(i, j kv.Key) bool {
	if e.desc {
	return i.Cmp(j) > 0
	}
	return i.Cmp(j) < 0
	})
	}

and

tidb/executor/batch_point_get.go

Line 353 in 0e068ed

slices.SortFunc(e.handles, less)

After support it, we could remove the codes below and update test cases.

tidb/planner/core/find_best_task.go

Lines 2551 to 2554 in 0e068ed

	// TODO: support keepOrder for partition table with dynamic pruning
	if ds.TableInfo().GetPartitionInfo() != nil && ds.SCtx().GetSessionVars().StmtCtx.UseDynamicPruneMode {
	return invalidTask
	}