Convert EditPage buttons, checkboxes and summary input to OOUI

Convert EditPage buttons, checkboxes and summary input to OOUI

Several methods now have a new implementation using OOjs UI widgets
(ButtonInputWidget/ButtonWidget, CheckboxInputWidget, TextInputWidget).
The existing (public) methods are unchanged. The OOjs UI version is
used by default.

Because this change can cause problems for extensions and on-wiki
scripts depending on the exact HTML, the old version is still available
and can be used by setting $wgOOUIEditPage = false; in LocalSettings.php.
This will be removed later and OOjs UI will become the only option.
To make testing easier, users can also force either mode by adding
&ooui=true or &ooui=false to the action=edit URL.

* EditPage::getSummaryInput() and EditPage::getSummaryInputOOUI()
* EditPage::getCheckboxes() and EditPage::getCheckboxesOOUI()
* EditPage::getCancelLink()
* EditPage::getEditButtons()

Bug: T111088
Co-Authored-By: Amir Sarabadani <ladsgroup@gmail.com>
Co-Authored-By: Florian Schmidt <florian.schmidt.welzow@t-online.de>
Change-Id: I25aa78ac59082789938ecfb5878eb16614392995