block: Add VMDK descriptor file parser for Flat createType

Adds parser for the Virtual Machine DisK descriptor
file. The parser supports 2 flat/pre-allocated create types,
monolithicFlat & twoGbMaxExtentFlat. The parser marks any other
type as unsupported.

The implementation references VMDK descriptor specification from
https://web.archive.org/web/20240527050638if_/https://www.vmware.com/app/vmdk/?src=vmdk

Signed-off-by: Sumedh Alok Sharma <sumsharma@microsoft.com>

block/src/formats/mod.rs

@@ -11,3 +11,4 @@ pub mod qcow;
 pub mod raw;
 pub mod vhd;
 pub mod vhdx;
+pub mod vmdk;