add fdroid isar build script (#2100)

Co-authored-by: Manuel K <manuel@kerk-net.de>

mobile/scripts/fdroid_build_isar.sh

@@ -0,0 +1,14 @@
+cd .isar
+bash tool/build_android.sh x86
+bash tool/build_android.sh x64
+bash tool/build_android.sh armv7
+bash tool/build_android.sh arm64
+mv libisar_android_arm64.so libisar.so
+mv libisar.so ../.pub-cache/hosted/pub.dev/isar_flutter_libs-*/android/src/main/jniLibs/arm64-v8a/
+mv libisar_android_armv7.so libisar.so
+mv libisar.so ../.pub-cache/hosted/pub.dev/isar_flutter_libs-*/android/src/main/jniLibs/armeabi-v7a/
+mv libisar_android_x64.so libisar.so
+mv libisar.so ../.pub-cache/hosted/pub.dev/isar_flutter_libs-*/android/src/main/jniLibs/x86_64/
+mv libisar_android_x86.so libisar.so
+mv libisar.so ../.pub-cache/hosted/pub.dev/isar_flutter_libs-*/android/src/main/jniLibs/x86/
+cd ..