Run default addressables build conditionally (#231)

* Add asmdef and Addressable content build in the builder

* Move asmdef content into its own directory

* Mark UnityBuilderAction as Editor-only

dist/default-build-script/Assets/Editor/UnityBuilderAction/Versioning/VersionGenerator.cs

@@ -0,0 +1,10 @@
+namespace UnityBuilderAction.Versioning
+{
+  public static class VersionGenerator
+  {
+    public static string Generate()
+    {
+      return Git.GenerateSemanticCommitVersion();
+    }
+  }
+}