BUG #18619: uppercase column with quotation marks, gets an error without quotation marks

The following bug has been logged on the website:

Bug reference: 18619
Logged by: Kirill N
Email address: gcso(at)sqliteonline(dot)com
PostgreSQL version: 17rc1
Operating system: docker 17rc1
Description:

Hello,

If you create a table with field names in uppercase and put them in
quotation marks.
then such fields can be accessed only with quotation marks.

postgres=# create table a ("b" int, "C" int);
CREATE TABLE
postgres=# select b from a;
b
---
(0 rows)

postgres=# select c from a;
ERROR: column "c" does not exist
LINE 1: select c from a;
^
postgres=# select C from a;
ERROR: column "c" does not exist
LINE 1: select C from a;
^
postgres=# select "c" from a;
ERROR: column "c" does not exist
LINE 1: select "c" from a;
^
postgres=# select "C" from a;
C
---
(0 rows)

The table structure is returned without quotation marks

postgres=# SELECT
t.table_schema,
t.table_name,
c.column_name,
c.data_type
FROM
information_schema.tables t
JOIN
information_schema.columns c
ON
t.table_schema = c.table_schema
AND t.table_name = c.table_name
WHERE
t.table_type = 'BASE TABLE'
AND t.table_schema NOT IN ('information_schema', 'pg_catalog') --
Исключаем системные схемы
ORDER BY
t.table_schema,
t.table_name,
c.ordinal_position;
table_schema | table_name | column_name | data_type
--------------+------------+---------------+-------------------
public | a | b | integer
public | a | C | integer