Building on Stable Rust without the `stable` feature

[chyyran]

As of #122, librashader can be built on stable Rust with the stable feature. This issue tracks building on stable Rust without features = ["stable"], which is mostly blocking on type_alias_impl_trait.

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Right now, librashader relies on the following features when not building with the stable feature.

Language features

• [ ] type_alias_impl_trait
• [ ] impl_trait_in_assoc_type
  • https://github.com/rust-lang/rust/pull/120700 This is being stabilized "soon"
• [x] ~~try_blocks (capi)~~ Removed in #121
• [x] ~~let_chains~~ Removed in #120

Polyfilled library features

• [x] ~~os_str_bytes~~ (Stabilized 1.74, MRSV is at 1.78)
• [x] extract_if
• [x] pointer_is_aligned (sptr), needed in capi (Stabilized 1.79, MSRV 1.78)
• [x] ~~strict_provenance (sptr) (gl for invalid, not really needed but good for semantics)~~ Removed in #102
• [x] ~~array_chunks~~ Removed in #103