code: func ExpressionsToPBList(sc *stmtctx.StatementContext, exprs []Expression, client kv.Client) (pbExpr []*tipb.Expr) {
  	pc := PbConverter{client: client, sc: sc}
  	for _, expr := range exprs {
  		v := pc.ExprToPB(expr)
  		pbExpr = append(pbExpr, v)
  	}
  	return
  }
docs: // ExpressionsToPBList converts expressions to tipb.Expr list for new plan.