Parser: lower property consumers to PROPERTY_REF.

Parser: lower property consumers to PROPERTY_REF.

Previously, the generator inferred reference intent from raw AST shape.

Now the parser marks the relevant property node as PROPERTY_REF before
building METHOD_CALL, assignment, or update nodes, and the generator
accepts both PROPERTY and PROPERTY_REF via
njs_generate_is_property_lvalue().

Introduce NJS_TOKEN_PROPERTY_REF as an explicit parser-side marker for
property accesses that carry reference semantics (assignment targets,
delete operands, increment/decrement, method-call receivers).