Problem/Motivation
In #2897638: Views exposed sort identifiers are not configurable, the exposed sort identifiers were made configurable in the same way as the exposed filters identifiers.
But if the sort is exposed, this "meta" sorting options are not configurable. They will always be sort_by and sort_order.
This is an issue if you have several views in the same page exposing different sort filters, as this will show "The submitted value changed in the Sort by element is not allowed." unless you have the same filter ids in both.
Proposed resolution
Allow the exposed sort identifiers when exposed to be configured, having sort_by and sort_order by default.
Remaining tasks
MR with tests.
User interface changes
New, when sorting is exposed show in the exposed sort configuration subform the id for the sort_by and sort_order ids.
API changes
TBD
Data model changes
Config schema change. Will require upgrade path.
Release notes snippet
When exposing the sort options in the exposed form, the site builder is able to configure the identifiers that are exposed in the URL as query parameter values.