Implement `ExtractIf`/`extract_if` feature

[CohenArthur]

We need to be able to handle the nightly extract_if feature for Rust-for-Linux, as it makes use of it

https://doc.rust-lang.org/nightly/std/vec/struct.ExtractIf.html

One difficulty will be once again to "fake" this feature as it is not present in core 1.49. I'm not sure how we're going to inject an entire module into the compiler so we need to figure that out as well.

I don't think there is that much code that we can't handle so that should be okay

[powerboat9]

I wonder if we couldn't just YOLO target rustc version bumps. Either that, or do minicore but the full 1.49 core extended with 1.85 core features.

[powerboat9]

Misc footgun notes (up to 1.72, seems to be when extract_if was renamed from drain_filter):

• https://blog.rust-lang.org/2021/05/11/edition-2021/#intoiterator-for-arrays
• https://blog.rust-lang.org/2021/07/29/Rust-1.54.0/#attributes-can-invoke-function-like-macros
• https://blog.rust-lang.org/2022/01/13/Rust-1.58.0/#captured-identifiers-in-format-strings
• I think 1.59 removes llvm_asm!, also https://blog.rust-lang.org/2022/02/24/Rust-1.59.0/
• https://blog.rust-lang.org/2022/05/19/Rust-1.61.0/#custom-exit-codes-from-main
• https://blog.rust-lang.org/2022/06/30/Rust-1.62.0/#default-enum-variants
• https://blog.rust-lang.org/2022/08/11/Rust-1.63.0/#turbofish-for-generics-in-functions-with-impl-trait
• https://blog.rust-lang.org/2022/09/22/Rust-1.64.0/#c-compatible-ffi-types-in-core-and-alloc
• https://blog.rust-lang.org/2022/11/03/Rust-1.65.0/
• https://blog.rust-lang.org/2022/12/15/Rust-1.66.0/#explicit-discriminants-on-enums-with-fields
• https://blog.rust-lang.org/2023/01/26/Rust-1.67.0/#must-use-effective-on-async-fn
• https://blog.rust-lang.org/2023/03/09/Rust-1.68.0/#default-alloc-error-handler
• https://blog.rust-lang.org/2023/07/13/Rust-1.71.0/
• (low priority diagnostic quality thing) https://blog.rust-lang.org/2023/08/24/Rust-1.72.0/#rust-reports-potentially-useful-cfg-disabled-items-in-errors

A jump all the way to 1.72 would be difficult, but it might be best to bite the bullet (depending on how bad it is). We have some support for multiple target rustc versions, so we could probably work on core 1.49 and 1.72 at the same time.

For now, we could find some way to patch core into a sort of mutant 1.49+72, but that would have its own problems and could make it harder to bump rustc versions unless done carefully.