Add example for *_build_test in xcschemes.top_level_anchor_target (#2950)

Also works around a bug for libraries that merged into other targets.

---------

Signed-off-by: Brentley Jones <github@brentleyjones.com>

Author: brentleyjones

examples/integration/Lib/BUILD

@@ -19,7 +19,7 @@ exports_files(
 
 ios_build_test(
     name = "ios_Lib",
-    minimum_os_version = "15.0",
+    minimum_os_version = "16.0",
     tags = ["manual"],
     targets = [":Lib"],
     visibility = ["@rules_xcodeproj//xcodeproj:generated"],

examples/integration/xcodeproj_targets.bzl

@@ -251,4 +251,17 @@ XCSCHEMES = [
             ],
         ),
     ),
+    xcschemes.scheme(
+        name = "ios_build_test",
+        run = xcschemes.run(
+            build_targets = [
+                xcschemes.top_level_anchor_target(
+                    "//Lib:ios_Lib",
+                    library_targets = [
+                        "//Lib",
+                    ],
+                ),
+            ],
+        ),
+    ),
 ]