In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.
This was done for indicators, targets and time splitting methods so that we
can get the string identifier and component in order to display a help_icon.
The functions were also made abstract, removing the default implementation.
Indicators, targets and time splitting methods should define this function.
Meirza