Add action to support only showing certain fields

Re-rolled patch #5 to work in 3.0.0

Did not try the patch, but the module already has similar functionality, as per the README:

While using a bulk_edit form display can work, it has two issues where:

1. This would limit to only one configuration of shown fields per entity bundle. This wouldn't work if you wanted to have 2 specific fields for one view, and 2 other fields for another view.
2. The default "Modify field values" action has checkboxes which reveal the form fields, where this patch would force users to populate the pre-chosen fields, which is ideal for certain situations.

I understand this is marked closed as designed, but I am just providing this patch in case others out there have the same use case. The issue can remain closed.

I would prefer the same solution as in D7, where it is possible from view to view to choose which fields should be editable.
Maybe patch #10 can do that? - I will try that when I get time.

"Works as designed" means that it works as intended, but I don't think it's designed well enough.
I have tested the solution described in the README and it works fine, but it is one and the same solution for all views, and that is not good, as different views may have different functional needs.

I hope that patch #10 solves the problem and that the module will be upgraded to meet everyone's needs.

I have taken the liberty of marking this as Active, as I think this module benefits from the expansion that has begun in #10.
I have installed the patch and it works!

There is a problem:
When I have selected an action and have to fill in the selection for the possible fields, options are included for fields that are not in the list:
I have selected two fields "Status for konto" and "Tilknytning til kursus". Both fields can only be assigned one value. However, below the fields, options appear for some fields that can contain multiple values. Se picture "Views_bulk_edit_selections.png".
The first "Change method" is for a multi-valued field. It is ok when the field is activated in views_bulk_edit, but not here.
The other "Change method" belong to fields that can only have one value, so they should not be displayed at all, and they should also not be displayed when the field is not activated in views_bulk_edit.