MySQL lowercases schema name in `database()` and `show databases` after `use <MixedCase>`

Creating and selecting a mixed-case schema is reflected as lowercase in MySQL, but Dolt returns the requested name.

## Dolt
```sql
# Welcome to the DoltSQL shell.
# Statements must be terminated with ';'.
# "exit" or "quit" (or Ctrl-D) to exit. "\help" for help.
10382/main> create schema Test;
Query OK, 1 row affected (0.02 sec)
10382/main> use Test;
Database Changed
Test/main> select database();
+------------+
| database() |
+------------+
| Test |
+------------+
1 row in set (0.00 sec)
```

## MySQL
```sql
mysql> drop schema Test;
Query OK, 0 rows affected (0.101 sec)

mysql> create schema Test;
Query OK, 1 row affected (0.063 sec)

mysql> use Test;
Database changed
mysql> select database();
+------------+
| database() |
+------------+
| test |
+------------+
1 row in set (0.004 sec)
```

Start by reproducing the CREATE SCHEMA, USE, SELECT DATABASE(), and SHOW DATABASES statements in the DoltSQL shell, then compare the results with MySQL for a mixed-case schema. Done means Dolt consistently matches MySQL's lowercasing behavior for the selected schema and database listing.

Written by the indexing model from the issue text.