Bump jni to 0.22 and migrate the Android JNI bridge

[Tryanks]

Supersedes #469.

jni 0.22 redesigned its environment and attachment model, so crates/android and crates/platform/gpui-android (excluded from the workspace, built as a path dependency of tcode-android) move together:

• Native method exports take EnvUnowned and run their JNI work through with_env(...).resolve::<LogErrorAndDefault>(), which also catches panics at the FFI boundary and logs errors instead of the previous silent if let Ok drops. Exports that never touch the environment keep their plain bodies.
• JavaVM::from_raw is now infallible and registers the singleton; scoped attach_current_thread()/get_env() become closure-based attach_current_thread(|env| …) (a no-op attachment on the Java main thread, which only pushes a local frame). JObject::from_raw now takes the Env.
• GlobalRef → Global<JObject<'static>> (no longer Clone, so JniObject holds it in an Arc).
• Method names and signatures use jni_str!/jni_sig! (compile-time MUTF-8/parsed signatures) instead of runtime &str; with_activity takes &'static JNIStr + MethodSignature.
• Deprecated env.get_string/get_array_length/get_int_array_region become JString::try_to_string, JPrimitiveArray::len/get_region; JString::from(JObject) becomes the checked JString::cast_local.
• jboolean is bool in jni-sys 0.4, so the u8 conversions go away.

Cargo.lock only re-points the two crates at jni 0.22.4 (already in the graph); jni 0.21.1 stays for its other consumer.

Local evidence (macOS arm64, NDK 27.1.12297006):

• RUSTFLAGS='-D warnings' CARGO_NDK_PLATFORM=26 cargo ndk -t arm64-v8a check -p tcode-android --locked ✅ (the CI "Mobile and web checks" command)
• cargo fmt --all --check ✅ (gpui-android formatted with rustfmt --edition 2024 since it is outside the workspace)
• cargo clippy --workspace --all-targets --locked -- -D warnings ✅
• cargo build --workspace --locked ✅
• cargo test -p tcode-android --locked ✅ (no tests)
• cargo machete ✅

Not covered: no Android device/emulator run; the JNI bridge behaviour (IME, clipboard, camera QR results, preview host) was verified by compilation only.