Ignore inherited object members in variable lookups

[feritcemkahraman]

An undefined $constructor currently expands to function Object() { [native code] } instead of triggering the undefined-variable error. $toString similarly produces invalid CSS even in silent mode. The only option also reads inherited object members as variable values.

Check own properties before resolving values in both lookup paths. Existing undefined-value handling and explicitly defined names such as $constructor remain supported; the check also works on the supported Node 14 runtime.

Validation:

• Three new regressions fail against the original source (39 passed, 3 failed).
• All 42 tests pass after the change, including explicit object-member variable names.
• c8: 100% statements, branches, functions and lines.
• Full ESLint and git diff --check pass.

No dependencies or public API were changed.