[Impeller] Build standalone library on Android. (#55566)

Fixes https://github.com/flutter/flutter/issues/156012

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index a865021..bb2ab9b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -153,6 +153,11 @@
     ]
   }
 
+  # Build the standalone Impeller library.
+  if (is_mac || is_linux || is_win || is_android) {
+    public_deps += [ "//flutter/impeller/toolkit/interop:library" ]
+  }
+
   if ((flutter_runtime_mode == "debug" || flutter_runtime_mode == "profile") &&
       (is_ios || is_android)) {
     public_deps += [ "//flutter/testing/scenario_app" ]
@@ -213,7 +218,6 @@
         "//flutter/impeller:impeller_dart_unittests",
         "//flutter/impeller:impeller_unittests",
         "//flutter/impeller/toolkit/interop:example",
-        "//flutter/impeller/toolkit/interop:library",
       ]
     }