[5.0][RFC] Move Toolbar singleton to HtmlDocument

[HLeithner]

This removes the usage of instances in the Toolbar Class and moves it to HtmlDocument.

Conceptional feedback would be helpful.

Summary of Changes

The reason moving is mainly because the HtmlDocument is everywhere where we need the toolbar and the toolbar is only relevant to the HtmlDocument.

Testing Instructions

For the moment only the smart search indexer has been
changed to use the new getToolbar function. But all other
toolbars also use the HtmlDocument thru the Toolbar::getInstance()
method.

Actual result BEFORE applying this Pull Request

toolbars are working

Expected result AFTER applying this Pull Request

toolbars still working

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[HLeithner]

Additional I was wondering about the rtl stuff and the arrow-left / arrow-right thing and if it is a good idea to do this in php. I think it would be better to move this to css and add direction aware icon for such cases like the back button.

[heelc29]

I have tested this item ✅ successfully on 29117ee

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[HLeithner]

Merging this to get more real live testing in next alpha and pbf