rust: use flate2 with C zlib

move flate2.rs to a backend supporting the setting
of window_bits, which is not the case for miniz-oxide.

This will allow WebSocket to use Sec-WebSocket-Extensions
which can set a non-default window_bits

rust/Cargo.toml.in

@@ -48,7 +48,7 @@ num = "~0.2.1"
 num-derive = "~0.4.2"
 num-traits = "~0.2.14"
 widestring = "~0.4.3"
-flate2 = "~1.0.19"
+flate2 = { version = "~1.0.19", features = ["zlib"] }
 brotli = "~3.4.0"
 hkdf = "~0.12.3"
 aes = "~0.7.5"