Blink: Fix compilation of cppgc_enable_object_names

With `cppgc_enable_object_names = true` GCInfo objects are not merged
into their base classes but kept as leaves to aid debugging. This
requires that types are destroyed through their leave classes.

Bug: chromium:1056170
Change-Id: I13ae76a594d342e2d37739a6fb4251d982f6fb38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3141722


Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918754}