adding cmake files to packaging

["Christian T. Steigies" <cts@debian.org>]

Hi,
a package that I maintain is switching from automake to cmake.  I had to
patch CMakeLists.txt a bit to make it compile on Debian, upstream used hand
written code to detect the Cairo and Pixman libraries, which does not work
for me, and I am not experienced enough with cmake to patch this code).  
I have replaced that with cmake files, for example as is used in fontforge or
freerdp2.

I wonder what is the correct (Debian) way to include external cmake files,
from what I see in other packages, using

https://codesearch.debian.net/search?q=FindCairo.cmake

these files seems to be provided by upstream and they seem to be using a
variety of different versions (functional mostly identical?).  I would place
the cmake files into a cmake or debian/cmake directory.  Does it matter
which one I use (license?  support for non-Linux systems?)?

Shouldn't there be a debian package that provides external cmake files for
packagers, or maybe include them in the lib-dev package that it is used for
(if they are not provided by cmake itself)?

thanks,
Christian