block: merge qcow, vhdx and block_util into block crate

This commit merges crates `qcow`, `vhdx` and `block_util` into the
crate `block`, which can allow `qcow` to use functions from `block_util`
without introducing a circular crate dependency.

This commit is based on crosvm implementation:
f2eecc4152

Signed-off-by: Yu Li <liyu.yukiteru@bytedance.com>

Cargo.toml

@@ -80,7 +80,7 @@ tracing = ["vmm/tracing", "tracer/tracing"]
 members = [
     "api_client",
     "arch",
-    "block_util",
+    "block",
     "devices",
     "event_monitor",
     "hypervisor",
@@ -89,12 +89,10 @@ members = [
     "option_parser",
     "pci",
     "performance-metrics",
-    "qcow",
     "rate_limiter",
     "serial_buffer",
     "test_infra",
     "tracer",
-    "vhdx",
     "vhost_user_block",
     "vhost_user_net",
     "virtio-devices",