src: move node::errno_string into node_errors.h/cc
Move node::errno_string
into node_errors.h/cc and move it into
the node:errors
namespace to reduce the size of the header.
It's not on any performance-critical code path so does not need
to be inlined.
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines