sql: support coercing string literals to arrays

[benesch]

In PostgreSQL, the following statement works fine:

#  select '["a", {"b":1}]'::jsonb #- '{1,b}';
 ?column?  
-----------
 ["a", {}]

CockroachDB complains

> select '["a", {"b":1}]'::jsonb #- '{1,b}';
pq: unknown signature: json_remove_path(jsonb, string)

unless you specifically make the RHS an array:

> select '["a", {"b":1}]'::jsonb #- array['1', 'b'];
+------------------+
| json_remove_path |
+------------------+
| ["a", {}]        |
+------------------+
> select '["a", {"b":1}]'::jsonb #- '{1,b}'::text[];
+------------------+
| json_remove_path |
+------------------+
| ["a", {}]        |
+------------------+

We should support automatically coercing string literals to arrays. According to @justinj this isn't trivial.

/cc @knz

[nstewart]

We just had a customer run into this. cc @jseldess since it looks like it won't be fixed for 2.0. cc @awoods187

[knz]

Complement: #24746

[knz]

see #33341

[awoods187]

See https://stackoverflow.com/questions/55047689/sum-of-differences-over-a-jsonb-array-field-in-cockroachdb/55048350#comment96898607_55048350