[Bug 54971] New: Update d3d12.idl with vkd3d PFN_D3D12_SERIALIZE_ROOT_SIGNATURE fix

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=54971

Bug ID: 54971
           Summary: Update d3d12.idl with vkd3d
                    PFN_D3D12_SERIALIZE_ROOT_SIGNATURE fix
           Product: Wine
           Version: unspecified
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: d3d
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Integrate the following fix from vkd3d:
https://source.winehq.org/git/vkd3d.git/commitdiff/6f1f14d97a9f7688d1c838060...
to https://gitlab.winehq.org/wine/wine/-/blob/master/include/d3d12.idl.

Currently, wine uses a slightly outdated version of d3d12.idl header. The main
point of this request is to update include/d3d12.idl header to be aligned with
vkd3d. I created it because it's kind of a blocker for:
https://github.com/ocornut/imgui/pull/4604.