Fix EZP-26501: In-edit Locations window (legacy) should not force "Visible" flag

[peterkeung]

JIRA issue ticket: https://jira.ez.no/browse/EZP-26501

Work done to address https://jira.ez.no/browse/EZP-22260 also included this specific commit, whose goal was to save the user's selection of the "hidden flag" toggle in the Locations window in edit mode:

c3e8ff5

However, that commit caused the following:

• "Visible" is the new default in the Locations window, not "Unchanged"
• "Visible" overrides any hide effort of a workflow
• Selecting "Unchanged" as a user and then saving the draft actually saves the selection as "Visible"

Given that:

• The Locations window in edit mode is only enabled for first drafts. (Ref: http://share.ez.no/learn/ez-publish/node-visibility-hiding-and-revealing-content/(page)/4#eztoc2634_0_4)
• A node's hidden flag is technically only hidden or not. (Hidden by superior is derived from the parent.)
• By default a node's hidden flag is "off".
• The use of the Locations window in edit mode is only for hiding the node; otherwise its hidden flag is technically "unchanged".
• The effects of the Locations window in edit mode are applied after the content/publish/after trigger.
• The effects of the Locations window can thus unexpectedly override a content/publish/after workflow if "Visible" is selected.

This is technically true:

• The "Visible" option is never valid (or at least not a more accurate description than "Unchanged"). Thus it should not be used.

=== How to test this fix ===

First, enable the Locations window: Select "on" for "Locations" under the "User preferences" panel in the right sidebar. Then test the following scenarios:

• Create a new draft. "Visibility after publishing" should give you the options of "Unchanged" or "Hidden". "Unchanged" should be default.
• Store the draft with "Unchanged" as the selection. Note that the selection is kept.
• Store the draft with "Hidden" as the selection. Note that the selection is kept.
• Edit an existing object. The selection should always show as "Unchanged".

[peterkeung]

Ping @pspanja @benkmugo for review

[benkmugo]

Nothing to add to the description from my end; all the details are there.
The main points are the last two under 'Given that', which explain the issue the commit introduced.

I'm currently working around the issue with an override template, but it would be good to have this fixed in the core.

+1