src: add AliasedStruct utility

For http2 (and eventually QUIC) we have a struct that is backed
by a v8::BackingStore and exposed to the JavaScript side as an
ArrayBuffer and TypedArray. This is similar to AliasedBuffer
except that it is fronted by a struct on the C++ side.

```c++
struct foo {
  uint32_t ex1;
  uint32_t ex2;
};

AliasedStruct<foo> foo_;

foo_->ex1 = 1;
foo_->ex2 = 2;

foo_.GetArrayBuffer();
```

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/32778


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>