In plugins/fs/android/src/main/java/FsPlugin.kt getFileDescriptor, for
uncompressed assets AssetManager.openFd returns an AssetFileDescriptor
whose parcel descriptor is the whole APK; its startOffset/length were
dropped and Rust read from offset 0, i.e. APK bytes. Only compressed
assets (openFd throws) took the cache copy path.
All assets now use the cache copy path. The cache file path is also checked
to stay below cacheDir/_assets. Kotlin not compiled here: unverified, needs
an on-device check.
