BUG #18057: unaccent removes intentional spaces

The following bug has been logged on the website:

Bug reference: 18057
Logged by: Martin Schlossarek
Email address: martin(at)schlossarek(dot)me
PostgreSQL version: 15.1
Operating system: Fedora 38
Description:

I discovered that the unaccent extension also removes intentional spaces
that are explicitly specified in the accent.rules. As far as I see it
correctly, all fraction characters are affected, for example:

```sql
# select unaccent('1½');
--- expected output: 1 1/2
--- actual output: 11/2
```

Affected characters:
```bash
$ curl -s
"https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob_plain;f=contrib/unaccent/unaccent.rules;hb=HEAD"
| grep -E " "
¼ 1/4
½ 1/2
¾ 3/4
⅐ 1/7
⅑ 1/9
⅒ 1/10
⅓ 1/3
⅔ 2/3
⅕ 1/5
⅖ 2/5
⅗ 3/5
⅘ 4/5
⅙ 1/6
⅚ 5/6
⅛ 1/8
⅜ 3/8
⅝ 5/8
⅞ 7/8
⅟ 1/
↉ 0/3
```