With the toolchain splitting namespaces, ostream.h's `operator<<`
templates aren't reliably found with name lookup, likely due to the loss
of associated namespaces (zygoloid commented on this at
https://github.com/carbon-language/carbon-lang/pull/3161#discussion_r1307941999).
This is especially a barrier to moving the lex files into `Carbon::Lex`;
versus other parts of the toolchain, they contain more printable types
which are used cross-namespace, including `Carbon::Testing`. As a
consequence, I'm looking at migrating ostream.h to a more reliable
approach that doesn't rely as much on everything being in the `Carbon`
namespace.
Replacing direct raw_string_ostream uses. I figure the wrapper should be used more consistently.
There are still remaining raw_string_ostream uses that weren't compatible -- I'm continuing to look at those, but felt it was cleaner to have this on its own.
This was bugging me after I saw all the strings; it feels like this is why we have EnumBase on the toolchain side.
I've included the move of EnumBase to //common because I figured it's reasonable to evaluate together; if we don't want EnumBase in this case, it doesn't make sense to move.
Jon Ross-Perkins