wix: include zstd.pyd in the installation

When trying to create a zstd bundle, the MSI based install said:

  abort: compression engine zstd could not be loaded

The Inno installer is unaffected.  The name will need to be updated to include
'cext' when merging into default.

contrib/wix/dist.wxs

@@ -18,6 +18,7 b''
           <File Name="mercurial.mpatch.pyd" />
           <File Name="mercurial.osutil.pyd" />
           <File Name="mercurial.parsers.pyd" />
+          <File Name="mercurial.zstd.pyd" />
           <File Name="pyexpat.pyd" />
           <File Name="bz2.pyd" />
           <File Name="select.pyd" />