feat(ext/ffi): Implement UnsafePointer and UnsafePointerView API

[eliassjogreen]

This pr adds support for passing, returning and reading pointers as proposed by the UnsafePointer and UnsafePointerView api (#12824).

Closes #12809, #12456, #12824 and #12752

[CLAassistant]

All committers have signed the CLA.

[eliassjogreen]

This pr could very easily implement UnsafePointer as proposed in #12824 if that is what we want. It would most likely make working with pointers way easier imo

[bnoordhuis]

I'm not sure using f64's is sound. V8 tends to canonicalize NaNs - maybe Infs and subnormals too, but definitely NaNs - which means there's a subset of the 64 bit space that's going to get corrupted.

You could maybe get away with it if it's only NaNs and Infs¹ but definitely not when it's subnormals too. An example of a subnormal is 0000 0000 0000 0001 (1u64 interpreted as f64.)

tl;dr Don't rely on V8 leaving the top 12 bits untouched, use BigInts instead.

¹ ARM64 and x86_64 have up to 52 address lines, which is exactly the f64 significand's size. NaNs and Infs are encoded in the exponent, not the significand.

[eliassjogreen]

@bnoordhuis internally pointers are now represented as the high and low bytes of an u64 ((u32, u32)) which should avoid the issues with transmuting pointers as f64. I also implemented the UnsafePointer API to make it easier to work with pointers although it should probably be looked through for my sanity and to make sure it all works as expected, cc @DjDeveloperr

[DjDeveloperr]

LGTM, got a few comments

[eliassjogreen]

This PR is ready for review now!

[bnoordhuis]

Nice work. Mostly LGTM.

[bnoordhuis]

Thanks Elias, LGTM.

[brandonros]

What next release can we expect this to land in? v1.17.0? When is that expected to land?

https://github.com/denoland/deno/milestone/28 currently says "past due 1 day" as of 2021-12-15

excited for this to land!!!

[DjDeveloperr]

Yes, it's going to be in 1.17.0 release which is a bit delayed it seems. Can expect it in a day or two I think

[lucacasonato]

@DjDeveloperr It is not delayed. 1.17.0 will release tomorrow as documented in the release schedule: https://deno.land/manual@v1.16.4/contributing/release_schedule. I have updated the milestone accordingly now.