For macOS platform, set "SqueakPluginsBuiltInOrLocalOnly" to "false"

...to expand lookup paths for external modules, which is needed for FFI.

See
- http://wiki.squeak.org/squeak/5846
- http://lists.squeakfoundation.org/pipermail/squeak-dev/2010-May/150498.html

This now matches the OSVM default:
- https://github.com/OpenSmalltalk/opensmalltalk-vm/blob/Cog/platforms/iOS/vm/OSX/Squeak-Info.plist

templates/macos/Squeak.app/Contents/Info.plist

@@ -550,7 +550,7 @@
 	<key>SqueakMouseOptionButton3</key>
 	<integer>2</integer>
 	<key>SqueakPluginsBuiltInOrLocalOnly</key>
-	<true/>
+	<false/>
 	<key>SqueakQuitOnQuitAppleEvent</key>
 	<false/>
 	<key>SqueakTrustedDirectory</key>