iris: android-app's Gradle shell, and the emulator run for I2

The Gradle side of RUST.md's I2: MainActivity, IrisView (extending
android-view's RustView with the two native methods it has no hook
for -- window insets, and unregistering this view's entry in
iris::android::insets's side table), and RustView.java/
RustInputConnection.java vendored from android-view (no published AAR
to depend on) with one deliberate diff noted in a comment: mViewPeer
is protected rather than package-private, so a subclass in a different
package can reach it.

Measured on the emulator (x86_64, API 26, SwiftShader Vulkan):
dumpsys input_method shows the served InputConnection is ours, and
Gboard's suggestion strip reads real buffer content back through
text_before_cursor ("hi | Hi | HI" after typing "hi") -- the same bar
E1 set, met. Not met: nothing draws. The clear colour reaches the
screen (confirmed by swapping it to magenta) and the layout engine
reports the correct widget count and pixel regions (log::debug! calls
left in view.rs's render() for exactly this), but no primitive shows
up, on both Vulkan/SwiftShader and GLES/virgl. Root cause not found;
one unconfirmed lead (a GLES-only D2/D2Array warning that could point
at the glyph atlas) is written up in RUST.md's I2 rather than chased
into core/src/render/, which is mid-flight in a separate benchmark
branch this session.

I2 is therefore built and wired but not tickable -- RUST.md has the
full writeup, what was ruled out, and where to pick this up.

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

iris/android-app/build.gradle

@@ -0,0 +1,3 @@
+plugins {
+    id("com.android.application") version "9.4.0" apply false
+}