iOS Modules: separate main platform code from modules

Moved previously builtin modules 'GameCenter', 'AppStore', 'iCloud' to separate modules to be represented as plugin.
Modified 'ARKit' and 'Camera' to not be builtin into engine and work as plugin.
Changed platform code so it's not affected by the move.
Modified Xcode project file to remove parameters that doesn't make any effect.
Added basic '.gdip' plugin config file.

modules/SCsub

@@ -47,7 +47,14 @@ for name, path in env.module_list.items():
 
     # Some modules are not linked automatically but can be enabled optionally
     # on iOS, so we handle those specially.
-    if env["platform"] == "iphone" and name in ["arkit", "camera"]:
+    if env["platform"] == "iphone" and name in [
+        "arkit",
+        "camera",
+        "camera_iphone",
+        "gamecenter",
+        "inappstore",
+        "icloud",
+    ]:
         continue
 
     lib = env_modules.add_library("module_%s" % name, env.modules_sources)