Give a phone without a Qualcomm SoC the generic WebGPU runtime

The APK's ONNX Runtime is the QNN build, which carries no WebGPU, so a
non-Qualcomm phone had nothing above the CPU provider. The APK now also
carries Microsoft's stock onnxruntime-android 1.29.0 (32 MB) as
libonnxruntime_generic.so, and the app offers it after the QNN build.

The runtime search stops at a perfect fit, so on a Qualcomm device the
QNN build — listed first — is all that is opened, and the generic build
never loads beside it. A Qualcomm SoC is read from ro.soc.manufacturer
or, before Android 12, from Qualcomm's FastRPC library being present:
a Qualcomm device mistaken for another would trade its Hexagon for the
generic rung.

apps/darkroom-android/src/lib.rs

@@ -451,8 +451,13 @@ fn unpack_bundled_models(app: &slint::android::AndroidApp) {
     // on a first launch they were not on disk until this line. The runtime
     // is in the APK's native library directory beside `libdarkroom.so`,
     // which is also where Qualcomm's DSP loader has to be pointed for the
-    // Hexagon skel (docs/dev/inference.md §3, §8).
-    dr_ui::inference::init(native_library_dir().into_iter().collect());
+    // Hexagon skel (docs/dev/inference.md §3, §8). Two of them: the QNN
+    // build, and the generic WebGPU build by its file name, which the
+    // engine opens only when the first does not fit the SoC (§3.2).
+    let runtimes = native_library_dir()
+        .map(|dir| vec![dir.clone(), dir.join("libonnxruntime_generic.so")])
+        .unwrap_or_default();
+    dr_ui::inference::init(runtimes);
 }
 
 /// The directory the system unpacked this APK's native libraries into.