wasi: simplify WASI memory management

This commit migrates the WASI C++ code from UncheckedCalloc()
to std::vectors.

PR-URL: https://github.com/nodejs/node/pull/33525


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>