fix: Make AWSPluginsCore public (#2472)

Author: palpatim

Package.swift

@@ -294,6 +294,10 @@ let package = Package(
             name: "Amplify",
             targets: ["Amplify"]
         ),
+        .library(
+            name: "AWSPluginsCore",
+            targets: ["AWSPluginsCore"]
+        ),
         .library(
             name: "AWSAPIPlugin",
             targets: ["AWSAPIPlugin"]