[iOS/GN] Fix ios_chrome_unittests to pass when build with gn.

Change compile_xib template to work with different types of xib
files (some do generate xxx.nib/... while other just generate a
single xxx.nib).

Add resources required by ios_chrome_unittests to the application
bundle including compiled native_content_controller_test.xib.

BUG=546283,459705

Review URL: https://codereview.chromium.org/1880393004

Cr-Original-Commit-Position: refs/heads/master@{#387264}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 2cb71a8ba37fd387113fb2b9f2407f750be158dc

config/ios/rules.gni

@@ -198,8 +198,7 @@ template("bundle_data_xib") {
       invoker.source,
     ]
     outputs = [
-      "$target_gen_dir/$_nib_filename/objects.nib",
-      "$target_gen_dir/$_nib_filename/runtime.nib",
+      "$target_gen_dir/$_nib_filename",
     ]
     args = [
       "--minimum-deployment-target",
@@ -220,11 +219,10 @@ template("bundle_data_xib") {
     public_deps += [ ":$_compile_xib" ]
 
     sources = [
-      "$target_gen_dir/$_nib_filename/objects.nib",
-      "$target_gen_dir/$_nib_filename/runtime.nib",
+      "$target_gen_dir/$_nib_filename",
     ]
     outputs = [
-      "{{bundle_resources_dir}}/$_nib_filename/{{source_file_part}}",
+      "{{bundle_resources_dir}}/$_nib_filename",
     ]
   }
 }