nofunc is the abstract null type, the equivalent of none but for the
function type hierarchy.
none and nofunc (and later on noextern) all can only represent a null
value, however their nulls are distinct (as there isn't any subtype
relationship between them).

Bug: v8:7748
Change-Id: Ic5ae502cc21a581ca2e0f5abc46139435d950af9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3805884Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82274}