Keep the correct case for the charset for canonical string

[dbussink]

The canonical string representation needs to keep the correct case for the charset. Those are never upcased in MySQL so we should not enforce that here either.

Related Issue(s)

Fixes #12104

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[shlomi-noach]

Should we enforce lower casing the charset though?

[dbussink]

Should we enforce lower casing the charset though?

We don't do that anywhere in the parser at the moment at all. We could maybe, but that's a whole different effort that goes beyond just the charset here, but applies to anything that's always lowercase and would need separate logic to be enforced then.

[GuptaManan100]

I don't think we should enforce the lower casing, because mixed case and upper case do work with MySQL -

mysql [localhost:5731] {msandbox} (test) > select convert('abc' using utf8mb4);
+------------------------------+
| convert('abc' using utf8mb4) |
+------------------------------+
| abc                          |
+------------------------------+
1 row in set (0.00 sec)

mysql [localhost:5731] {msandbox} (test) > select convert('abc' using UTF8mb4);
+------------------------------+
| convert('abc' using UTF8mb4) |
+------------------------------+
| abc                          |
+------------------------------+
1 row in set (0.00 sec)

mysql [localhost:5731] {msandbox} (test) > select convert('abc' using UTF8MB4);
+------------------------------+
| convert('abc' using UTF8MB4) |
+------------------------------+
| abc                          |
+------------------------------+
1 row in set (0.00 sec)