Is your feature request related to a problem? Please describe.

There is no layout field for plugins in the standard field types.
https://docs.joomla.org/Standard_form_field_types

Describe the solution you'd like

What I would like to see is a Plugin Layout field added. This would allow me to select a layout like i can in components and modules.

Additional context

Why would i want this?

• Parity with components and modules. Both Components and Modules have a layout field which is useful.
• There are times this can be useful. The most basic example is that your plugin replaces a shortcode with some content.
  • If I can select a layout, I can chooses to either have a dark or light theme
  • A user can choose what content to display in place of the shortcode

I have emulated this field using the filelist filed.

<field 
    name="layout"
    type="filelist"					
    default="default.php"
    label="PLG_CONTENT_HELLOWORLD_LAYOUT_LABEL"
    description="PLG_CONTENT_HELLOWORLD_LAYOUT_DESC"
    directory="plugins/content/helloworld/tmpl"
    filter=""
    exclude="\.html$"
    stripext="1"
    hide_none="1"
    hide_default="0"
/>