zsh: improve shell{,Global}Aliases

This commit changes the way aliases are rendered, adding the "no more
flags" flag `--`, which means that, for example, the alias `"-" = "cd
-";` will work as expected. (I was getting a syntax error before this
change.)

Additionally, now the alias key is shell escaped, which may help some
edge cases. I'm honestly not sure if this part is necessary since I
assume an alias can't contain spaces anyway, but it definitely
shouldn't break anything.

tests/modules/programs/pls/zsh.nix

@@ -23,10 +23,10 @@ with lib;
       assertFileExists home-files/.zshrc
       assertFileContains \
         home-files/.zshrc \
-        "alias ls='@pls@/bin/pls'"
+        "alias -- 'ls'='@pls@/bin/pls'"
       assertFileContains \
         home-files/.zshrc \
-        "alias ll='@pls@/bin/pls -d perms -d user -d group -d size -d mtime -d git'"
+        "alias -- 'll'='@pls@/bin/pls -d perms -d user -d group -d size -d mtime -d git'"
     '';
   };
 }