Disallow assigning reference to unset readonly property

Closes GH-7942
Closes GH-8188

Add missing scope check for readonly prop initialization

If the initializing assignment is an array append we will go through
the UNDEF codepath of get_property_ptr_ptr, which did not ve

Add missing scope check for readonly prop initialization

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.

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