Link dialog option button is not keyboard operable

Started a PR at https://github.com/xwiki/xwiki-platform/pull/3714

Some notes I took while looking for a solution:
infoTab.add -> https://github.com/ckeditor/ckeditor4/blob/82796d03d0ebbe34d48f3b65c6dde27107812a51/plugins/dialog/plugin.js#L2046 returns [CKEDITOR.dialog.definition.uiElement](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_dialog_definition_uiElement.html) !== [CKEDITOR.ui.dialog.uiElement](https://ckeditor.com/docs/ckeditor4/latest/api/CKEDITOR_ui_dialog_uiElement.html)
addFocusable -> https://github.com/ckeditor/ckeditor4/blob/82796d03d0ebbe34d48f3b65c6dde27107812a51/plugins/dialog/plugin.js#L1491 takes argument CKEditor.DOM.Element

CKEDITOR.ui.dialog.uiElement . getElement() --> CKEditor.DOM.Element

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Using the button event type did not work, tried with things like:
return {
id: 'optionsToggle',
type: 'button',
className: 'linkOptionsToggle',
label: '<span class="arrow arrow-right"></span> ' +
CKEDITOR.tools.htmlEncode(editor.localization.get('xwiki-link.options')),

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Click triggered twice when pressing keyboard:

https://github.com/ckeditor/ckeditor4/blob/82796d03d0ebbe34d48f3b65c6dde27107812a51/plugins/dialog/plugin.js#L710-L713 weird keyboard listener sending an extra click event...