re-add blank schemas file

Author: jbelkins

Sources/SmithyCodegenCore/CodeGenerator.swift

@@ -6,6 +6,7 @@
 //
 
 import struct Foundation.Data
+import class Foundation.FileManager
 import class Foundation.JSONDecoder
 import struct Foundation.URL
 
@@ -26,7 +27,15 @@ public struct CodeGenerator {
         let modelData = try Data(contentsOf: modelFileURL)
         let astModel = try JSONDecoder().decode(ASTModel.self, from: modelData)
 
-        // In the future, AST will be used to create a Model
-        // Model will be used to generate code
+        // In the future, AST will be used to create a Model.
+        // Model will be used to generate code.
+
+        // This code simply writes an empty schemas file, since it is expected to exist after the
+        // code generator plugin runs.
+        //
+        // Actual code generation will be implemented here later.
+        if let schemasFileURL {
+            FileManager.default.createFile(atPath: schemasFileURL.path, contents: Data())
+        }
     }
 }