Add mocker for JInput
[fix] Restore support for rendering custom fieldsets on 'joomla.edit.params'. Fixes #4284

Retrieve all fieldsets instead of params and attribs only

Define ignore_fieldsets consistently

Add ignore_fieldsets

Code style

Further implementation of ignore_fieldsets

Restore options tabs in com_content

Update modal.php with related changes to restore support for rendering custom fieldsets when using JLayout 'joomla.edit.params'

Update modal.php with related changes to restore support for rendering custom fieldsets when using JLayout 'joomla.edit.params'
Doc blocks in the mockers
Merge branch 'staging' of github.com:joomla/joomla-cms into staging
Add methods to retrieve mock input object
Inject the mock input object in the Application tests