Move ZSTD_getCParamsFromCCtxParams() out of its C forwarding body and
export the original symbol from the Rust parameter API. The Rust-side
ABI mirror already has layout checks, so it can project the same fields
to the existing scalar policy leaf without exposing additional context
state. Keep the exclusion mask in C and query it from Rust so reduced
builds retain their preprocessor-selected block-compressor behavior.
Test Plan:
- `cc -fsyntax-only -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dict -Ilib/legacy lib/compress/zstd_compress.c` -- passed.
- `cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed.
- `git diff --check` and `git diff --cached --check` -- passed.
- Heavy Cargo, Make, native, and test-suite verification intentionally not run per request.
ddidderr
3f081ee53b