buildRustCrate: set CARGO_FEATURE_* when running the build script

Cargo sets `CARGO_FEATURE_*` for all features when running a build
script:

https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-build-scripts

Some crates have build scripts (e.g. openblas-src) that rely on the
feature variables being properly set.

Since we now need several representations of features, this change
also updates `createFeatures` to be a list of features, rather than
`rustc` feature arguments. `configureCrate` and `buildCrate` then
build the required representations as-needed.

Fixes #68978