sql: support transactionally dropping an index and creating one with the same name

[ajwerner]

Is your feature request related to a problem? Please describe.
Today, if you try this, you'll get an error.

root@localhost:26257/defaultdb> create table foo (i int primary key, j int);
CREATE TABLE
root@localhost:26257/defaultdb> create index idx on foo(j);
CREATE INDEX
root@localhost:26257/defaultdb> begin;
BEGIN
root@localhost:26257/defaultdb  OPEN> drop index idx;
NOTICE: the data for dropped indexes is reclaimed asynchronously
HINT: The reclamation delay can be customized in the zone configuration for the table.
DROP INDEX
root@localhost:26257/defaultdb  OPEN> create index idx on foo(j);
ERROR: index "idx" being dropped, try again later
SQLSTATE: 55000

Describe the solution you'd like
It should just work. The declarative schema changer will make this straightforward.

Additional context
This is hard to fix in the legacy schema changer.

Jira issue: CRDB-25297

[Jolg42]

(Random find) I could reproduce this on CockroachDB v23.1

And I opened a separate issue for columns #109587