Use built-in functions for elvish (#7025)

Currently the elvish shell integration uses the `hostname` command, this
may not exist on all systems and is somewhat redundant to rely on when
elvish has an
[`platform:hostname`](https://elv.sh/ref/platform.html#platform:hostname)
function that can be used and will work across platform regardless of
command availability. On top of this instead of directly calling the
`pwd` function we can simply use the built-in
[`$pwd`](https://elv.sh/ref/builtin.html#$pwd) variable that elvish
gives us. This should prevent the shell integration from breaking due to
external function availability.

src/shell-integration/elvish/lib/ghostty-integration.elv

@@ -75,7 +75,8 @@
   }
 
   fn report-pwd {
-    printf "\e]7;file://%s%s\a" (hostname) (pwd)
+    use platform
+    printf "\e]7;file://%s%s\a" platform:hostname $pwd
   }
 
   fn sudo-with-terminfo {|@args|