block: Rename AsyncDiskFile::new_async_io to create_async_io

The new_ prefix in Rust conventionally denotes constructors that return
Self (e.g. Vec::new(), File::new()). AsyncDiskFile::new_async_io does
not return Self. It is a factory method that constructs and returns a
Box<dyn AsyncIo> worker bound to the disk file descriptor and
metadata. The create_ prefix communicates this: the caller receives
a freshly constructed object of a different type.

This rename touches every format backend in block plus two external
callers in virtio-devices and performance-metrics. Every change is a
mechanical s/new_async_io/create_async_io/ substitution. No functional
change.

Ref: #7877 (task 3.2.8)
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

block/src/fixed_vhd_sync.rs

@@ -70,7 +70,7 @@ impl disk_file::AsyncDiskFile for FixedVhdDiskSync {
         Ok(Box::new(FixedVhdDiskSync(self.0.clone())))
     }
 
-    fn new_async_io(&self, _ring_depth: u32) -> BlockResult<Box<dyn AsyncIo>> {
+    fn create_async_io(&self, _ring_depth: u32) -> BlockResult<Box<dyn AsyncIo>> {
         let size = self
             .0
             .logical_size()