Add optional symlinks for .framework/Headers and .framework/Modules

The placement spec has these as optional, but allowed:
https://developer.apple.com/documentation/bundleresources/placing_content_in_a_bundle#3875936

The open source Apple code created Headers:
https://opensource.apple.com/source/CF/CF-368.28/framework.make.auto.html

gomobile has historically created Modules, and it's optional, so let's keep that to minimize issues for existing users/scripts

Author: scosman

cmd/gomobile/bind_iosapp.go

@@ -313,6 +313,8 @@ func frameworkLayoutForTarget(t targetInfo, title string) (*frameworkLayout, err
 			symlinks: map[string]string{
 				"A":                                      "Versions/Current",
 				"Versions/Current/Resources":             "Resources",
+				"Versions/Current/Headers":               "Headers",
+				"Versions/Current/Modules":               "Modules",
 				filepath.Join("Versions/Current", title): title,
 			},
 		}, nil