Draft: Updates fmt library to its latest version 7.1.3

This MR updates the fmt library to its latest version (7.1.3)

I have taken into account that there has been some custom changes into the fmt library header files in the past years.

With this command I was able to find the commits which brought changes:

# c5dc86c1 is the commit of the last update of the version of fmt
→ git log --oneline c5dc86c1..for/vtk-m -- include/diy/fmt include/diy/thirdparty/
cf12846 (origin/enforce-c++14, enforce-c++14) Enforce c++14 version
21fde7d Fix nvcc compile issue with the format library
e9a24b8 Enable stricter warnings and fix them
c4d2470 Pull upstream fix in i/d/fmt for the Intel compiler
23aafc0 Add FMT_HEADER_ONLY back in

I then proceed to cherry-pick/patch/manual apply each of the commit to the latest version of fmt.h, however, some of the changes brought by those commits were not longer necessary as there were already fixed in upstream fmt.

Find each of those cherry-pick /patch apply as individual commits in this MR