[4.0] Moving reusable parts of blankstate layout to a JLayout

[Bakual]

Pull Request for Issue #33279 .

Summary of Changes

• Moved the repeating parts of the layout to a JLayout which can be used also by 3rd parties.
• Added permissions checks for the "Add xxx" button. The permissions checks are kept as similar as reasonable to the one for the toolbar button
• Corrected the link of the "Add xxx" button to point to the respective controller task instead of directly going to the view.
• Adjusted the language strings for the "_CONTENT" so they only differate in the prefix. This could also be changed to "_ITEMS" but I think basically everything is "content" of some sort as well, not only com_content items. In the end, the name of the string doesn't matter anyway much.
• Move the "Learn More" string to the joomla.ini file, because this one always is the same.

Testing Instructions

Check the newly introduced blankstate layouts. They should look the same before and after this PR.

Documentation Changes Required

Should be included in the documentation about blankstate layouts when/if/once that exists

[Bakual]

One thing I wondered: The "Learn More" link currently opens in the same tab. Maybe it makes more sense to open it in a new tab? Since I guess usually the people going to read the help page don't actually want to leave the admin backend.

[brianteeman]

From an accessibility perspective it is OK to open a new window in this case because the content is designed to be read with the web page. This is even an example use case in the WCAG docs

[Bakual]

I've added target="_blank" to the help link so it opens in a new tab.

[Bakual]

Please can you check #33286 which was done at the same time as your great work to see if either of us needs to change much (other than the normal complete refactoring) due to the addition of the extension part.

I think from a first look of it, it should work fine with this PR

[Bakual]

adding target=_blank gives this horrid icon, its not even inline pixel perfectly...

Didn't even notice this, but you're right. It doesn't look nice. Open for suggestions (could also be done in a separate PR).

[joomdonation]

I have tested this item ✅ successfully on 17298b6

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[alikon]

RTC

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[richard67]

Thanks!