Joomla's version data is currently manipulable within a JVersion instance since the data is defined as public facing vars. This PR blocks the ability of developers to be able to manipulate this information by defining the version data as constants instead.

Backward Compatibility

Fetching Data

A magic getter is implemented which will catch any calls which tried to access the previously defined class member variables and will return the corresponding constant instead. A deprecation log message is added for these cases. In instances where someone trying to access an undefined class variable occurs, a E_USER_NOTICE PHP error is generated (similar to PHP's native handling).

Setting Data

With this PR, it's no longer possible. It should have never been possible. But, since we are being so strict on B/C, this must be highlighted. And we should hopefully not use the argument that a developer could previously overwrite the core platform's version data as an excuse to not accept this patch IMO.

Testing Instructions

Make sure you have the version data displayed in the admin toolbar (default yes), apply the patch, and make sure the page loads without any error messages.