shell_integration/windows: Add a manually-increased build number

shell_integration/windows: Add a manually-increased build number

Since this isn't yet built together with the rest, we can't reliably
use the client version without having to rebuilt the extension manually
on each release. But it would still be nice to be able to tell if a user
has the right version or not loaded, so instead just tag each update of
the DLLs with a separate release version.

This means that every time we update those binaries we'll have to manually
increment the number in the header, but worst case we'll forget from time
to time but we'll be able to know if we didn't, and know if we can rely on
the number or not.