release-23.1.0: opt: hoist uncorrelated equality subqueries

[mgartner]

Backport 1/1 commits from #100881.

/cc @cockroachdb/release

---

opt: hoist uncorrelated equality subqueries

Subqueries that are in equality expressions with a variable are now
hoisted. When these expressions exist in a filter, hoisting the subquery
can allow the main query to plan a lookup join, rather than an
inefficient full-table scan.

For example, consider the table and query:

CREATE TABLE t (
  a INT,
  INDEX (a)
);

SELECT * FROM t WHERE a = (SELECT max(a) FROM t);

Prior to this commit, the query plan for this query required a full
table scan:

select
 ├── columns: a:1
 ├── scan t@t_a_idx
 │    ├── columns: a:1
 │    └── constraint: /1/2: (/NULL - ]
 └── filters
      └── eq
           ├── a:1
           └── subquery
                └── scalar-group-by
                     ├── columns: max:9
                     ├── scan t@t_a_idx,rev
                     │    ├── columns: a:5
                     │    ├── constraint: /5/6: (/NULL - ]
                     │    └── limit: 1(rev)
                     └── aggregations
                          └── const-agg [as=max:9, outer=(5)]
                               └── a:5

By hoisting the subquery, the full table scan is replaced with a lookup
join:

project
 ├── columns: a:1
 └── inner-join (lookup t@t_a_idx)
      ├── columns: a:1 max:9
      ├── key columns: [9] = [1]
      ├── scalar-group-by
      │    ├── columns: max:9
      │    ├── scan t@t_a_idx,rev
      │    │    ├── columns: a:5
      │    │    ├── constraint: /5/6: (/NULL - ]
      │    │    └── limit: 1(rev)
      │    └── aggregations
      │         └── const-agg [as=max:9, outer=(5)]
      │              └── a:5
      └── filters (true)

This hoisting is disabled by default, but can be enabled by setting the
optimizer_hoist_uncorrelated_equality_subqueries session setting to
true.

Fixes #83392
Informs #51820
Informs #93829
Informs #100855

Release note (performance improvement): Queries that have subqueries in
equality expressions are now more efficiently planned by the optimizer when
optimizer_hoist_uncorrelated_equality_subqueries is set to true.

---

Release justification: We're backporting this to 22.2, so we'll need it
to work in 23.1.0 as well.

[cockroach-teamcity]

This change is 

[rytaft]

Reviewed 10 of 10 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner)

[mgartner]

Let's not backport this to 23.1.0. Closing.