Expose portstartupitem::loaded without portstartupitem_run

Closes: https://trac.macports.org/ticket/74185

src/port1.0/portstartupitem.tcl

@@ -5,6 +5,10 @@
 package provide portstartupitem 1.0
 
 namespace eval portstartupitem {
+    proc loaded {} {
+        package require portstartupitem_run
+        return [_loaded]
+    }
 }
 
 #   Newly added keys:

src/port1.0/portstartupitem_run.tcl

@@ -296,7 +296,7 @@ proc startupitem_create {} {
 
 # Check if this port's startupitems are loaded
 # Returns: list of loaded startupitems
-proc loaded {} {
+proc _loaded {} {
     set launchctl_path ${::portutil::autoconf::launchctl_path}
     if {$launchctl_path eq ""} {
         # assuming not loaded if there's no launchctl