block: aligned: Add seeking cursor and drop RawFile

RawFile wrapped AlignedFile only to add a seek position and the file
trait impls that the qcow and vhost_user_block code expects. Fold that
position and every impl onto AlignedFile so the wrapper layer goes away
and callers work with a single O_DIRECT aware file type.

AlignedFile now tracks a cursor and implements Read, Write, Seek,
WriteZeroesAt, PunchHole, FileSync, SeekHole, BlockBackend, Clone,
AsRawFd and AsFd in addition to the positional FileExt path. The
direct_io flag is dropped because alignment already encodes it, where
a zero alignment means the file was not opened with O_DIRECT.

All RawFile uses in the qcow internals and vhost_user_block move to
AlignedFile, and raw_file.rs is removed.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

block/src/lib.rs

@@ -15,7 +15,7 @@ pub mod factory;
 mod io_impl;
 pub use io_impl::{async_io, fcntl, request};
 pub(crate) mod aligned_buffer;
-pub(crate) mod aligned_file;
+pub mod aligned_file;
 pub mod formats;
 mod sparse;
 use std::alloc::{Layout, alloc_zeroed};
@@ -29,6 +29,7 @@ use std::path::Path;
 use std::str::FromStr;
 use std::{cmp, mem, result};
 
+pub use aligned_file::AlignedFile;
 use formats::qcow::internal as qcow;
 #[cfg(feature = "io_uring")]
 use io_uring::{IoUring, Probe, opcode};