src: allow custom PageAllocator in NodePlatform

For certain embedder use cases there are more complex memory allocation
requirements that the default V8 page allocator does not handle.
For example, using MAP_JIT when running under a hardened runtime
environment on macOS. This allows embedders like Electron to provide
their own allocator that does handle these cases.

PR-URL: https://github.com/nodejs/node/pull/38362


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>