Move UniFile to kotlinx-io FileSystem abstraction

[revonateB0T]

Mostly we use UniFile to

• Fastly send file (i.e. Linux sendfile syscall ), avoid copying content over JVM heap
• Common FileSystem functions(lookup children, create new children)
• Obtain its FileDescriptor and let libarchive do fast extraction
• Obtain its FileChannel to do DirectByteBuffer based operation

Where okio FileSystem only provide a ByteArray based, Java IO liked interface, no efficient platform IO primitives

Seems kotlinx-io will support these usage https://github.com/Kotlin/kotlinx-io/issues/241