to anonymous namespace.

While basegfx::internal::putNumberCharWithSpace is only used in
exportToSvgD, move it into the anonymous in the same file for
later enhancement.

Change-Id: I6534ac39b2095ed2ba12acc114c75737ad8dacb6
Reviewed-on: https://gerrit.libreoffice.org/58847
Tested-by: Jenkins
Reviewed-by: Mark Hung <marklh9@gmail.com>