Editing a preferences page in object mode is setting undesired values to some configurations

Steps to reproduce:

• create a new page: PageName
• acces it's administration (from the kebab menu) - this will create the WebPreferences page, with no value set
• manually access the object editor for this page (by typing /edit/PageName/WebPreferences?editor=object from the URL)
• without making any changes, save the document

Expected result:

• nothing changes in the page, a new entry appears in the history of the page but there are no changes between the previous version and the current one in history
  Actual result:
• some properties change from empty value to a set value ( * ). This is problematic because, even if the set value is the "default value"- which is not always the case -, this breaks inheritance of the properties from the higher level.

( * ) which properties change values and what values are set has changed a lot with the versions of XWiki (see comments and related issues). On 8.4.6, the values included the color theme , icon theme, default editor, etc, while on 12.2.1 the only properties that still change value seem to be "Enable extra accessibility features" and "Default page syntax" and "Obfuscate Email Addresses " (see screenshot )

This issue should be considered as a task to audit all the properties in XWikiPreferences and make sure their displayers always honor the set value, so that loading them in the object editor does not change the value.