[BoundsSafety] combining `single` and `counted_by` prints weird in attr-only mode

[hnrklssn]

typedef int * __single _Nonnull baz_t;
void bar(int len, baz_t __counted_by(len) p);

ends up being dumped as bar 'void (int, int * __counted_by(len) _Nonnull__single)'.
In -fbounds-safety it's (more reasonably) dumped as bar 'void (int, int *__single __counted_by(len) _Nonnull)'

The representation of these types may change as we upstream single, so probably not very high priority, but when we upstream we should try to handle this properly.