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
  • Stabilize associated type position impl Trait (ATPIT) rust-lang/rust#120700 This is being stabilized "soon"
• try_blocks (capi) Removed in capi: remove dependency on try_blocks #121
• let_chains Removed in Replace use of let_chains with other methods #120

Polyfilled library features

• os_str_bytes (Stabilized 1.74, MRSV is at 1.78)
• extract_if
• pointer_is_aligned (sptr), needed in capi (Stabilized 1.79, MSRV 1.78)
• strict_provenance (sptr) (gl for invalid, not really needed but good for semantics) Removed in ABI v2 #102
• array_chunks Removed in optimizations and improvements #103

[chyyran]

We should just move stable to default. TAITs are nowhere close to being stabilized, and C header generation is fundamentally broken with not much attention on fixing: mozilla/cbindgen#1107