PR #776 fixed an issue with complex aliases and expansion. However, this change
also introduced a problem with aliases which contain `]` (for example, commonly
seen on macOS: `alias ]=open`), due to using an associative array `seen_alias`,
indexed by the alias name. Due to `"$seen_alias[$arg]"`, it would fail when
`$arg` is expanded to anything containing `]`'. Thus, typing `] /` would result
in:
```
> ] /
(anon):unset:3: seen_alias[]]: invalid parameter name
```
This change fixes the issue by ensuring we properly access keys in the
associative array `seen_alias`.
Older versions of zsh have issues with map keys having special
characters, especially lacking ways to remove such keys. The
issue is described in detail in
https://unix.stackexchange.com/questions/626393/in-zsh-how-do-i-unset-an-arbitrary-associative-array-element.
This fix uses proposal from
[zsh-workers/43269](https://www.zsh.org/mla/workers/2018/msg01073.html),
discovered by Stephane Chazelas, that boils down to avoid removing keys
from the map, and reconstruct the map anew with some keys omitted.
Co-authored-by: @phy1729
