AnyRsetView: Refactor the columns_name method and update doc. We drop the 'label_column_%s' % colidx pattern and add a clean column_label method that might be overwritten by children class to alter the way default columns headers are computed.

[facets] FacetFilterMixIn: add documention for class and generate_form There is also a small refactoring to make the code clearer. An intermediate variable is introduced and the call is reindented to make it clearer. No logic change.

[facet] Add infered type restriction to Filtered result set (closes #1988776) This does not alter the result while allowing more selection option on other variable than the filtered one.

[source] remove uicfg rule for dropped synchronizing attribute

backport stable

[datafeed] remove remaining uses of 'synchronizing' attribute replaced by 'in_synchronization' in 3.13.8. Closes #1989131

[datafeed parser] only update an entity attributes when needed. Closes #1989142 This may avoid error with some entities which have immutable attributes and don't check something actually changed. Also, avoid modifying the cached item representation, this may cause pb when an item is seen several times during an import.

backport stable

[schema] drop erroneous default on CWSource.in_synchronization. Closes #1990585

[forms] fix bug in linkto refactoring (misordered arguments)