fix(builtin.commands): no preview for multiline description commands (#2244)

(cherry picked from commit 22e13f6f69)

lua/telescope/make_entry.lua

@@ -1240,7 +1240,7 @@ function make_entry.gen_from_commands(opts)
       attrs,
       entry.nargs,
       entry.complete or "",
-      entry.definition,
+      entry.definition:gsub("\n", " "),
     }
   end