Replace platform-intrinsic with core_intrinsics

[sagudev]

Make pathfinder_simd work on latest nightly.

Fixes #558

[fredizzimo]

Unfortunately, this broke the build on non-nightly Arm64 builds, since std::intrinsics::simd is a nightly only feature.
https://doc.rust-lang.org/std/intrinsics/simd/index.html

0.5.2 of pathfinder_simd works fine.

[sagudev]

Unfortunately, this broke the build on non-nightly Arm64 builds, since std::intrinsics::simd is a nightly only feature.

All std::intrinsics::simd usage is hidden behind pf_rustc_nightly, so it should still compile.

[fredizzimo]

Then I'm not sure what's going on, because use std::intrinsics::simd::*; in simd/src/arm/mod.rs is included. And it's causing the following error in our CI

error[E0432]: unresolved import `std::intrinsics::simd`
  --> /Users/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/pathfinder_simd-0.5.3/src/arm/mod.rs:13:22
   |
13 | use std::intrinsics::simd::*;
   |                      ^^^^ could not find `simd` in `intrinsics`

https://github.com/neovide/neovide/actions/runs/10007814471/job/27663280524

And downgrading to 0.5.2 of pathfinder_simd fixed the issue (this commit) neovide/neovide@89448f5

Unfortunately, I don't have a mac and I did not manage to easily setup cross compilation for ARM (neither linux or apple-darwin on my Linux machine, so I'm not able to reproduce the issue by compiling this repository alone. I can probably make it to work but it requires some more effort.

[sagudev]

https://github.com/neovide/neovide/actions/runs/10007814471/job/27663280524#step:3:78:

note that the toolchain 'nightly-2023-09-30-x86_64-apple-darwin' is currently in use (overridden by '/Users/runner/work/neovide/neovide/rust-toolchain.toml'

So actually CI uses nightly and the problem is it uses too old nightly version.

[fredizzimo]

Thanks. I thought I had deleted the rust-toolchain.toml file a long time ago, but it must have come back with some rebase or merge. Sorry for the false report.