iOS: add AppIcon asset name to Xcode project

The current work-flow for adding app icons to an
iOS app during deployment is not good. You basically
need to specify that you want to use asset catalogs
from within Xcode and add your icons there. The
problem is that qmake will regenerate the Xcode project
the next time it runs, and your changes will then be lost.

This patch will check if the project has a valid asset
catalog assigned to QMAKE_BUNDLE_DATA, and configure
the Xcode project to use it for app icons.

Change-Id: I06621ca46aad91de96cb23ba8ca3b1a3f1226670
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>

mkspecs/macx-ios-clang/features/default_post.prf

@@ -174,6 +174,21 @@ macx-xcode {
     ios_device_family.value = $$QMAKE_IOS_TARGETED_DEVICE_FAMILY
     QMAKE_MAC_XCODE_SETTINGS += ios_device_family
 
+    # If QMAKE_BUNDLE_DATA contains an asset catalog that includes an
+    # AppIcon.appiconset, we configure Xcode to use it for app icons.
+    for(bundle_data, QMAKE_BUNDLE_DATA) {
+        for(bundle_file, $${bundle_data}.files) {
+            !contains(bundle_file, .*\.xcassets$): next()
+            !exists($$absolute_path($$bundle_file/AppIcon.appiconset, $$_PRO_FILE_PWD_)): next()
+
+            asset_catalog_appicon.name = "ASSETCATALOG_COMPILER_APPICON_NAME"
+            asset_catalog_appicon.value = "AppIcon"
+            QMAKE_MAC_XCODE_SETTINGS += asset_catalog_appicon
+            break()
+        }
+        !isEmpty(asset_catalog_appicon.name): break()
+    }
+
     # Set up default 4-inch iPhone/iPod launch image so that our apps
     # support the full screen resolution of those devices.
     launch_image = Default-568h@2x.png