This removes object auto-vivification support.
This also means that we can remove the corresponding special
handling for typed properites: We no longer need to check that a
property is convertible to stdClass if such a conversion might
take place indirectly due to a nested property write.
Additionally OBJ_W style operations now no longer modify the
object operand, and as such we no longer need to treat op1 as a
def in SSA form.
The next step would be to actually compile the whole LHS of OBJ_W
operations in R rather than W mode, but that causes issues with
SimpleXML, whose object handlers depend on the current compilation
structure.
Part of https://wiki.php.net/rfc/engine_warnings.
If op1 is ERROR the behavior is to not perform any assignment and
return NULL. However, if the RHS was a by-value returning function,
we'd instead emit a notice and return the RHS as the return value
(even though the value was not assigned to anything -- the temporary
is immediately destroyed).
This normalized the behavior to always check for an ERROR in op1
first.
