fix(types): validate symbolic parameter defaults

[nahime0]

Summary

This replaces the approach proposed in #468 with post-schema semantic validation for symbolic parameter defaults.

infer_expr_type_syntactic classifies every ScopedConstantAccess as Str. Accepting Enum::Member solely because the receiver name matches the declared object type would therefore bypass validation and also accept missing enum cases or scalar class constants.

This PR instead:

• defers direct scoped-constant parameter defaults while class-like schemas are being built;
• resolves them semantically after class, interface, and enum metadata is complete, reusing infer_scoped_constant_access;
• distinguishes enum cases, class constants, and undefined symbols;
• preserves the declaring-class context for named, self::, static::, and parent:: receivers;
• covers unused functions, methods and constructors, constructor promotion, and closures;
• keeps plain property enum defaults out of scope because their EIR lowering is still incomplete.

Testing

• cargo build
• cargo test --test codegen_tests accepts_enum_case
• cargo test --test codegen_tests enum_case_default
• cargo test --test error_tests enum_case_parameter_default_rejects_missing_case
• cargo test --test error_tests object_parameter_default_rejects_scalar_class_constant
• cargo test --test error_tests plain_property_enum_case_default_remains_unsupported
• cargo test --test codegen_tests interface_promoted_property_accepts_object_default
• cargo test --test error_tests promoted_property_rejects_incompatible_object_default
• git diff --check

Related: #468