release-20.2: opt: prevent cycle in memo created by SplitDisjunction

[mgartner]

Backport 1/1 commits from #58434.

/cc @cockroachdb/release

---

opt: prevent cycle in memo created by SplitDisjunction

Previously, the SplitDisjunction rule would reuse table and column IDs
from the rule's input expressions in the left side of the generated
UnionAll expression. This was incorrectly believed to be safe. The
addition of partial indexes has provided an example that highlights the
flaw: this can create cycles in the memo.

Consider the table and query below:

CREATE TABLE t (
  k INT PRIMARY KEY,
  a INT,
  b INT,
  c INT,
  INDEX tab_c_idx (c) WHERE a > 1 OR b > 1
)

SELECT * FROM t WHERE a > 1 OR b > 1

This leads to a cycle in the memo because tab_c_idx can be scanned to
retrieve rows where a > 1 and where a > 1 OR b > 1. Notice the cycle
in the memo below: G2 -> G6 -> G10 -> G2. G2 includes both an
unconstrained partial index scan a DistinctOn created by
SplitDisjunction. The child of the DistinctOn is a UnionAll (G7)
with a left child of G10. G10 has two expressions, one of which is a
Select with an input of G2.

memo
 ├── G1: (scalar-group-by G2 G3)
 ├── G2: (select G4 G5) (scan t@tab_c_idx) (distinct-on G6 G7)
 ├── G3: (aggregations G8)
 ├── G4: (scan t)
 ├── G5: (filters G9)
 ├── G6: (union-all G10 G11)
 ├── G7: (aggregations G12)
 ├── G8: (count-rows)
 ├── G9: (or G13 G14)
 ├── G10: (select G4 G15) (select G2 G15)
 ├── G11: (select G16 G17)
 ├── G12: (const-agg G18)
 ├── G13: (eq G19 G20)
 ├── G14: (eq G18 G20)
 ├── G15: (filters G13)
 ├── G16: (scan t)
 ├── G17: (filters G21)
 ├── G18: (variable b)
 ├── G19: (variable a)
 ├── G20: (const 1)
 ├── G21: (eq G22 G20)
 └── G22: (variable b)

In order to prevent this cycle, SplitDisjunction now creates new table
and column IDs for both its left and right inputs. I've been unable to
find an example where table and column ID reuse in
SplitDisjuctionAddKey causes problems, but I've updated that rule to
err on the side of caution.

Fixes #58390

Release justification: This is a critical fix for a bug that causes
errors querying tables with disjunctive filters that are the same or
similar to the predicate of one of the table's partial indexes.

Release note (bug fix): A bug has been fixed which caused errors when
querying a table with a disjunctive filter (an OR expression) that is
the same or similar to the predicate of one of the table's partial
indexes.

[cockroach-teamcity]

This change is 

[rytaft]

Reviewed 5 of 5 files at r1.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner)