Closes#438
**Fixes:**
- Return the actual primary key instead of the rowid when the primary
key is not a rowid alias
sqlite:
```
limbo> create table foo (pk TEXT PRIMARY KEY, value);
sqlite> insert into foo values ('one', 'payload');
sqlite> insert into foo values ('two', 'payload');
sqlite> select * from foo;
one|payload
two|payload
```
limbo now:
```
limbo> create table foo (pk TEXT PRIMARY KEY, value);
limbo> insert into foo values ('one', 'payload');
limbo> insert into foo values ('two', 'payload');
limbo> select * from foo;
one|payload
two|payload
```
limbo before:
```
limbo> select * from foo;
1|payload
2|payload
```
Then, discovered two issues when running the whole TCL test suite
against a copy of `testing.db` that does not have rowid aliases in the
tables:
- Fix trying to convert a Scan into an IndexSearch when the associated
Expr refers to a different instance of the same table in a self-join
- Fix `scan_loop_body_labels` being pushed to in different parts of the
codegen for Scan/Search nodes resulting in incorrect label resolutions
**Additions:**
- Add a new db `testing/testing_norowidalias.db` that is a carbon copy
of `testing/testing.db` except the `id` columns of `users` and
`products` are not rowid aliases (i.e. they are `INT PRIMARY KEY`
instead of `INTEGER PRIMARY KEY`
- Run all TCL tests against both test databases with `do_execsql_test`
```
(testing/testing.db) Running test: coalesce-from-table
(testing/testing_norowidalias.db) Running test: coalesce-from-table
(testing/testing.db) Running test: coalesce-from-table-column
(testing/testing_norowidalias.db) Running test: coalesce-from-table-column
(testing/testing.db) Running test: coalesce-from-table-multiple-columns
(testing/testing_norowidalias.db) Running test: coalesce-from-table-multiple-columns
(testing/testing.db) Running test: glob-fn
(testing/testing_norowidalias.db) Running test: glob-fn
(testing/testing.db) Running test: where-glob
(testing/testing_norowidalias.db) Running test: where-glob
(testing/testing.db) Running test: where-glob-question-mark
(testing/testing_norowidalias.db) Running test: where-glob-question-mark
```
- Allow running tests against specific db file with
`do_execsql_test_on_specific_db $path`
- Wondering if I should add a new table with e.g. text primary key and
add some db-specific tests on that table...?
Closes#449
Mimics SQLite's EXPLAIN QUERY PLAN pretty printer.
Example run on a preexisting db:
```
$ cargo run /tmp/srn "explain query plan select * from t natural join t join t2 on t.id = 2*t2.id where t.id in (select * from t);"
QUERY PLAN
`--JOIN ON t.id = 2 * t2.id
|--JOIN
| |--SCAN t FILTER t.id IN (SELECT * FROM t)
| `--SCAN t
`--SCAN t2
```
Fixes https://github.com/penberg/limbo/issues/295
