[shell] Init script affects the behavior of Anchor element

I noticed in [init.ts](https://github.com/tauri-apps/tauri-plugin-shell/blob/v2/guest-js/init.ts#L21) that there's a click event listener on anchor elements, triggering a shell open.

I'm using Tiptap (a text editor), and there's a scenario where clicking on anchor elements during editing doesn't trigger default behavior. But now tauri directly invokes shell open.

Perhaps it would be beneficial to add some checks, such as whether the parent element is contenteditable or something