Allow links to open content in Offcanvas tray without edit mode being enabled.

Problem/Motivation

During #2820135: Allow any contextual link to opt-in to being displayed via offcanvas it was found that any link that uses the offcanvas tray always triggers Edit Mode.
To do #2815831: Move Off-canvas related CSS from drupal.outside_in library to drupal.off_canvas we need to separate the Offcanvas dialog from the Edit Mode as implemented in Settings tray module.

Currently any link that uses the offcanvas tray will trigger Edit Mode.

Proposed resolution

Introduce new link attribute data-outside-in-edit.

Remaining tasks

User interface changes

API changes

To trigger edit mode using offcanvas:

$mylink['attributes'] = [
      'class' => ['use-ajax'],
      'data-dialog-type' => 'dialog',
      'data-dialog-renderer' => 'offcanvas',
      'data-outside-in-edit' => TRUE,
    ];

Data model changes