fix: persist original file path when using bases (#672)

* fix: persist original file path when using bases

Prior to this change, the resulting lock file was called `<bases[0]>.lock`,
instead of `<filename>.lock`.

This change ensures the final, merged state has the correct `.FilePath`.

* test: Assert proper FilePath in layered HelmState

pkg/state/create.go

@@ -148,6 +148,8 @@ func (c *StateCreator) ParseAndLoad(content []byte, baseDir, file string, envNam
 		return nil, err
 	}
 
+	state.FilePath = file
+
 	return state, nil
 }