util: mark classes while inspecting them

This outlines the basic class setup when inspecting a class.

The implementation is a bit tricky but it should cover all edge cases.

Fixes: #32270 (closed)

Signed-off-by: Ruben Bridgewater ruben@bridgewater.de

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines