internal: set up Zig on CI and start using it in rust-analyzer

[lnicola]

🙃

[BenjaminBrienen]

What does this do and what motivated it? Is this just to avoid using C?

[lnicola]

When you cross-compile Rust, you still need a target-specific linker, and those aren't always easy to find. In addition, if you build e.g. on Ubuntu 24.04, your binary won't work on older distros. So every couple of years we used to bump the minimum required GLIBC, which caused a number of people to complain that they stopped working on unsupported distros like Debian oldoldstable, or CentOS/EL, which are even older.

cargo-zigbuild works as a linker and knows stuff about what's in each version of GLIBC, so we can build every Linux binary on ubuntu-latest while targeting the lovely EL8 vintage.