iris: add the android-app cdylib crate (I2, part 3)

iris/android-app is the concrete app RUST.md's I2 is judged against:
JNI_OnLoad, a Client implementing AndroidAppState, and new_view_peer
wrapping iris::android::new_peer's generic function in the plain
function pointer register_view_class needs. Its UI is tabs-ui::build,
unchanged from the winit example.

Deliberately excluded from the iris workspace (iris/Cargo.toml's new
`exclude`): android-view needs the NDK sysroot to link, so folding this
crate in would break `cargo build --workspace --all-targets` on the
host. It resolves as its own single-crate workspace instead, built
with `cd iris/android-app && cargo ndk -t x86_64 -P 26 build`.

Verified: cross-compiles and clippys clean for x86_64-linux-android
API 26; the host iris workspace (build/clippy/fmt/19 tests) is
unaffected. Not yet built: the Gradle shell (IrisView.java,
MainActivity, AndroidManifest) to actually install and run this on the
emulator -- next in RUST.md's I2.

Co-Authored-By: Claude Sonnet <noreply@anthropic.com>

iris/Cargo.toml

@@ -49,6 +49,13 @@ tabs-ui = { path = "tabs-ui" }
 
 [workspace]
 members = ["core", "macro", "tabs-ui"]
+# android-app pulls in android-view, which needs the NDK sysroot to link
+# -- excluded so `cargo build --workspace --all-targets` on the host stays
+# buildable. Cross-compile it from its own directory (its own single-crate
+# workspace, since it has no `[workspace]` table of its own and this
+# exclusion stops it inheriting this one): `cd android-app && cargo ndk
+# -t x86_64 -P 26 build`.
+exclude = ["android-app"]
 
 [workspace.package]
 version = "0.1.0"