Add visibility parameters to control scope of generated extension

Sources/ResgenSwift/Fonts/FontOptions.swift

@@ -7,6 +7,7 @@
 
 import ArgumentParser
 import Foundation
+import ToolCore
 
 // swiftlint:disable no_grouping_extension
 
@@ -21,6 +22,13 @@ struct FontsOptions: ParsableArguments {
     @Option(help: "Tell if it will generate static properties or methods")
     var staticMembers: Bool = false
 
+    @Option(
+        name: .customLong("visibility"),
+        help: "Visibility of extension and properties. Possibles values: public, private, package, internal. Default is internal",
+        completion: .list(["public", "private", "package", "internal"])
+    )
+    var extensionVisibility: ExtensionVisibility = .internal
+
     @Option(help: "Path where to generate the extension.", transform: { $0.replaceTiltWithHomeDirectoryPath() })
     var extensionOutputPath: String