nix: package outputs of build in .aar file

Add nix `result` folder to gitignore also.

Referenced issue:
* https://github.com/waku-org/nwaku/issues/3232

.gitignore

@@ -76,3 +76,6 @@ coverage_html_report/
 .qmake.stash
 main-qt
 waku_handler.moc.cpp
+
+# Nix build result
+result

flake.nix

@@ -51,6 +51,7 @@
           src = self;
           targets = ["libwaku-android-arm64"]; 
           androidArch = "aarch64-linux-android";
+          abidir = "arm64-v8a";
           zerokitPkg = zerokit.packages.${system}.zerokit-android-arm64;
         };
         default = libwaku-android-arm64;

nix/default.nix

@@ -10,6 +10,7 @@
     "x86_64-linux" "aarch64-linux"
   ],
   androidArch,
+  abidir,
   zerokitPkg,
 }:
 
@@ -32,6 +33,7 @@ in stdenv.mkDerivation rec {
   buildInputs = with pkgs; [
     openssl
     gmp
+    zip
   ];
 
   # Dependencies that should only exist in the build environment.
@@ -62,6 +64,7 @@ in stdenv.mkDerivation rec {
   ANDROID_NDK_HOME="${pkgs.androidPkgs.ndk}";
   NIMFLAGS = "-d:disableMarchNative -d:git_revision_override=${revision}";
   XDG_CACHE_HOME = "/tmp";
+  androidManifest = "<manifest xmlns:android=\"http://schemas.android.com/apk/res/android\" package=\"com.example.mylibrary\" />";
 
   makeFlags = targets ++ [
     "V=${toString verbosity}"
@@ -98,8 +101,10 @@ in stdenv.mkDerivation rec {
   '';
 
   installPhase = ''
-    mkdir -p $out/build/android
-    cp -r ./build/android/* $out/build/android/
+    mkdir -p $out/jni
+    cp -r ./build/android/${abidir}/* $out/jni/
+    echo '${androidManifest}' > $out/jni/AndroidManifest.xml
+    cd $out && zip -r libwaku.aar *
   '';
 
   meta = with pkgs.lib; {