fast_float implements C++17 from_chars for floating-point types, which
is still unavailable even in the latest versions of compilers e.g. for
macOS. It is maintained, unlike dtoa; it is said to be adopted as the
from_chars implementation for gcc. It is header-only, which simplifies
many things.
Change-Id: I6b597d4d35a076930e6e35f4f8cff3ca84f48ba1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/191248
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
