Because of how name builders used to lazy gather namespaces on the first
requested name, the objects were self mutating. As such only non-const
references could be used to pass them around.
Since that is no longer the case, this restores most of lost const
qualifiers.
This commit moves stuff around to enforce complete information being
present by the time the "Internal" assembly output is ready.
Because of that, the "Internal" format needed to change, now it uses
tag representation close to PTML as opposed to the one close to LLVM's
used before now.
Giacomo Vercesi