Add completions for FreeBSD's kldunload

Lists currently loaded kernel modules as valid completions, and obtains
a description via the newly minted `__fish_whatis` if available.

CHANGELOG.md

@@ -69,6 +69,7 @@ This section is for changes merged to the `major` branch that are not also merge
   - `j` (autojump #4344)
   - `jhipster` (#4472)
   - `kldload`
+  - `kldunload`
   - `meson`
   - `ngrok` (#4642)
   - `optipng`

share/completions/kldunload.fish

@@ -0,0 +1,12 @@
+function __fish_list_loaded_klds
+	set -l klds (kldstat | string match -r '\b\S+.ko$')
+	for kld in $klds
+		if set -l description (__fish_whatis (string replace '.ko' '' -- $kld) "kernel module")
+			printf '%s\t%s\n' $kld $description
+		else
+			printf '%s\n' $kld
+		end
+	end
+end
+
+complete -c kldunload -xa '(__fish_list_loaded_klds)'