Add specialization of Evaluate<> for Lazy_exact_nt

[afabri]

Summary of Changes

PR #8052 did not solve the problem reported in Issue #7934
This PR adds a partial specialization of Evaluate<> for Lazy_exact_nt, which derives from Lazy,
but the partial specialization for Lazy is not taken.

Todo: Generate a testcase that reproduces the reported issue, so that we check before/after.

Release Management

• Affected package(s): Polygon_2
• Issue(s) solved (if any): fix Access Violation on CGAL::Intersect with specific inputs #7934
• License and copyright ownership: unchanged

[sloriot]

Successfully tested in CGAL-6.0.1-Ic-351