[planbuilder] sort expression aliases always referenced

[max-hoffman]

This fixes a bug where a sort expression alias computed in the lower projection fails to index the nested expression.

Below, the first plan's sort searches for c5:6 in the child, but only finds a:7. The second plan fixes the correctness issue. Obviously there are more desirable projection organizations that version two, but this is small enough of an edge case that I think rewriting projection management with proper expression interning would be overkill right now. The rest of the plan tests look OK/improvements.

select distinct abs(c5) as a from one_pk where c2 in (1,11,31) order by a

before: 

Sort(abs(one_pk.c5:6)->a:7 ASC nullsFirst)
 └─ Distinct
     └─ Project
         ├─ columns: [abs(one_pk.c5:1)->a:0]
         └─ Filter
             ├─ HashIn
             │   ├─ one_pk.c2:0
             │   └─ TUPLE(1 (tinyint), 11 (tinyint), 31 (tinyint))
             └─ ProcessTable
                 └─ Table
                     ├─ name: one_pk
                     └─ columns: [c2 c5]

after:

Distinct
 └─ Project
     ├─ columns: [abs(one_pk.c5:5)->a:0]
     └─ Sort(a:6 ASC nullsFirst)
         └─ Project
             ├─ columns: [one_pk.pk:0!null, one_pk.c1:1, one_pk.c2:2, one_pk.c3:3, one_pk.c4:4, one_pk.c5:5, abs(one_pk.c5:5)->a:0]
             └─ Filter
                 ├─ HashIn
                 │   ├─ one_pk.c2:2
                 │   └─ TUPLE(1 (tinyint), 11 (tinyint), 31 (tinyint))
                 └─ ProcessTable
                     └─ Table
                         ├─ name: one_pk
                         └─ columns: [pk c1 c2 c3 c4 c5]

[jycor]

LGTM