Expand the native Link fieldtype functionality to include a label (with fallback) and new window toggle

[aaronbushnell]

The native Link fieldtype is great, but I think a couple additions could really make it considerably better while preserving backwards compatibility!

1. Add an accompanying "Label" field: When filled out, this could override the "inherited" title from a selected asset or entry. For example, {{ link_field:label }} is your custom label (if one exists). If one doesn't exist then it falls back to the title of the selected entry or asset.
2. Add a new window toggle: While checking if a link is_external is nice, it's not always the reason a client wants something to open in a new window. Putting this into a dedicated control would simplify this.

With this setup, I think the following Antlers API would work great—

<!-- The URL for backwards compatibility -->
{{ link_field }}

<!-- The custom label or the title of the asset/entry -->
{{ link_field:label }}

<!-- A boolean based on the New Window selection -->
{{ link_field:new_window }}

<!-- A shorthand combination for common CTAs <a href="https://example.com" class="px-3 py-1 font-bold">Label</a> -->
{{ link_field:el class="px-3 py-1 font-bold" }}