[5.2] Removing deprecated access to User object attributes

[Hackwar]

Summary of Changes

This PR removes almost all cases where we are accessing attributes of the user object through the deprecated CMSObject::get() method. All these can be replaced by simply accessing the attribute directly. This change is based on a check with phpstan.

Testing Instructions

Codereview

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

[sandewt]

I have tested this item ✅ successfully on eefbe1a

---

_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43268.}

[pe7er]

Thanks @Hackwar !