The AsmType class uses a design similar to the old Object* model, where
arbitrary values (including 0) are reinterpret_cast to pointers. This
yields the following UBSan error, among others:

    src/asmjs/asm-parser.cc:2000:51: runtime error: member call on null
    pointer of type 'v8::internal::wasm::AsmType'

This patch does the smallest possible fix by turning the affected methods
into static functions. Longer-term, we should consider switching the
overall class design to a "struct wrapping an Address" model like the new
Object definition, which is a bit non-trivial because some AsmType types
are ZoneObject subclasses.

Bug: v8:3770
Change-Id: Ie2a7cdc9eab32c4c469d699212c84b0419480b4f
Reviewed-on: https://chromium-review.googlesource.com/c/1397663Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58586}