runtime(vim9): remove extra escaping in Open

Before 71fd19d7ac this function went
through a `:!` command on all platforms, so it needed special escaping for `#` and
others. After that commit it doesn't go through that path on unix
platforms. Then with 48581f2ba9 this
escaping was re-added on unix and it's needs since it goes through
`sh -c`, but it should not have the extra escaping specific to `:!`.

Specifically my original broken command is:

```
PATH=/usr/bin:/bin VIMRUNTIME=~/dev/vim/runtime ./src/vim -u NONE -c 'call dist#vim9#Open("https://github.com/keith/dotfiles/blob/7bce9f5c697df6a549cf97bf5606d8b639e5bf5a/vimrc#L19")'
```

Where the `#L19` ends up being opened as `%5C#L19`. But I verified this
case still works as well:

```
PATH=/usr/bin:/bin VIMRUNTIME=~/dev/vim/runtime ./src/vim -u NONE -c 'call dist#vim9#Open("foo bar.txt")'
```

Which is what would otherwise break if we weren't doing any shell
escaping on unix.

closes: #19996

Signed-off-by: Keith Smiley <keithbsmiley@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/autoload/dist/vim9.vim

@@ -3,7 +3,7 @@ vim9script
 # Vim runtime support library
 #
 # Maintainer:   The Vim Project <https://github.com/vim/vim>
-# Last Change:  2026 Apr 06
+# Last Change:  2026 Apr 17
 
 export def IsSafeExecutable(filetype: string, executable: string): bool
   if empty(exepath(executable))
@@ -139,7 +139,11 @@ export def Open(file: string)
     setlocal shell&
     defer setbufvar('%', '&shell', shell)
   endif
-  Launch($"{Viewer()} {shellescape(file, 1)}")
+  if has('unix') && !has('win32unix') && !exists('$WSL_DISTRO_NAME')
+    Launch($"{Viewer()} {shellescape(file)}")
+  else
+    Launch($"{Viewer()} {shellescape(file, 1)}")
+  endif
 enddef
 
 # Uncomment this line to check for compilation errors early