Previously registration was case preserving, but lookup used
lowercased reporter name, so a reporter whose name contained
upper case character could not be requested by the user.
Doing this removes `<map>` from the include set of the base reporter
interface, and thus from bunch more TUs. This provides about 1.5%
improvements in the debug build of the static library, and 1% in
release build.
This should improve the compilation times by decreasing the number
of TUs compiled, without making overly big TUs that would cause
problems with heavy-tailed compilation times.
There is one "combined TU" for the top level part, and each subpart,
except for Reporters, which currently do not have any trivial TUs.
Martin Hořeňovský