Add a standalone construct_class() function that builds a class from
a ClassBlueprint and an Executable, replacing the virtual dispatch
through ClassElement::class_element_evaluation() with a direct switch
on ClassElementDescriptor::Kind.
This function reads pre-compiled SharedFunctionInstanceData indices
from the blueprint, creates ECMAScriptFunctionObjects at runtime, and
handles all class element types: methods, getters, setters, fields
(with initializers), and static initializers.
The function exists but is not yet called. No behavioral change.
