We used to allocate major numbers quite randomly, with no common place
to look them up if needed.
This commit is changing that by placing all major number allocations
under a new C++ namespace, in the API/MajorNumberAllocation.h file.
We also add the foundations of what is needed before we can publish this
information (allocated numbers for block and char devices) to userspace.
These changes are compatible with clang-format 16 and will be mandatory
when we eventually bump clang-format version. So, since there are no
real downsides, let's commit them now.
