[Impeller] Switched to static linked libc++ in vulkan validation layers. (#48290)

fixes flutter/flutter#138535
test coverage: existing integration tests in flutter repo which look for validation layers

I also verified locally that the `libc++.so` is no longer present and that it runs correctly.

```
$ find lib/arm64-v8a/
lib/arm64-v8a/
lib/arm64-v8a//libflutter.so
lib/arm64-v8a//libVkLayer_khronos_validation.so
```

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: gaaclarke

build/secondary/third_party/vulkan_validation_layers/BUILD.gn

@@ -464,7 +464,7 @@ foreach(layer_info, layers) {
     }
     if (is_android) {
       libs = [
-        "c++",  # Note: C++ added by Flutter.
+        "c++_static",  # Note: C++ added by Flutter.
         "log",
         "nativewindow",
       ]

shell/platform/android/BUILD.gn

@@ -499,13 +499,9 @@ action("android_jar") {
       "--native_lib",
       rebase_path("$validation_layer_out_dir/libVkLayer_khronos_validation.so"),
     ]
-    if (current_cpu == "arm64") {
-      args += [
-        "--native_lib",
-        rebase_path("$android_libcpp_root/libs/arm64-v8a/libc++_shared.so",
-                    root_build_dir),
-      ]
-    } else {
+    if (current_cpu != "arm64") {
+      # This may not be necessarily required anymore. It was kept to maintain
+      # old behavior.
       assert(false, "Validation layers not supported for arch.")
     }
   }