$obj->ro[] = 42;, passByRef($obj->ro); and the likes should emit an indirect
modification error message. This message already existed but was used
inconsistently.
Use a shared non-terminal for all class modifiers. This avoids conflicts when
adding modifiers that are only valid for certain targets. This change is
necessary for asymmetric visibility but might be useful for other future
additions.
Closes GH-9926
If the initializing assignment is an array append we will go through
the UNDEF codepath of get_property_ptr_ptr, which did not verify
that the initialization scope is valid.
Add support for readonly properties, for which only a single
initializing assignment from the declaring scope is allowed.
RFC: https://wiki.php.net/rfc/readonly_properties_v2
Closes GH-7089.
