Add IVssBackupComponents and related VSS backup interfaces

Include vsbackup.h in the VSS partition to expose IVssBackupComponents,
IVssBackupComponentsEx/Ex2/Ex3/Ex4, IVssExamineWriterMetadata/Ex/Ex2,
IVssWMComponent, and factory functions (CreateVssBackupComponentsInternal,
CreateVssExamineWriterMetadataInternal, etc.).

The header was previously excluded with the comment that it contains
C++ classes instead of COM interfaces, but the types are standard COM
interfaces (IUnknown-derived with pure virtual methods) declared using
C++ class syntax with __declspec(uuid(...)). ClangSharp handles these
correctly.

Inline wrapper functions (CreateVssBackupComponents, etc.) are excluded
since they are not DLL exports - the *Internal variants are the real
exports and are already mapped to VSSAPI.dll in libMappings.rsp.

Fixes #2095

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jevansaks

generation/WinSDK/Partitions/VSS/main.cpp

@@ -17,7 +17,7 @@
 #include <vss.h>
 #include <vswriter.h>
 #include <vsmgmt.h>
-//#include <vsbackup.h> This contains C++ classes instead of COM interfaces
+#include <vsbackup.h>
 #include <vsadmin.h>
 #include <vsprov.h>
 #include <vsserror.h>

generation/WinSDK/Partitions/VSS/settings.rsp

@@ -4,8 +4,15 @@ CreateWriter
 CVssWriterEx
 CreateWriterEx
 CVssWriterEx2
+CreateVssBackupComponents
+CreateVssExamineWriterMetadata
+IsVolumeSnapshotted
+VssFreeSnapshotProperties
+GetProviderMgmtInterface
+ShouldBlockRevert
 --traverse
 <IncludeRoot>/um/vsadmin.h
+<IncludeRoot>/um/vsbackup.h
 <IncludeRoot>/um/vsmgmt.h
 <IncludeRoot>/um/vsprov.h
 <IncludeRoot>/um/vss.h