Attach a resolution hint to this unbound type reference.
Only
#isValidHint() hints can be accepted. The given source indicates the
quality of this hint. The
VarianceInfo indicate how the hint was used and
how it was expected to be used. A hint from a co-variant location may not have the same impact
for a contra-variant usage as a contra-variant hint. Consider a return type of a method
<T> Collection<? extends T> m(..) { }
and its usage
Collection<? super CharSequence> variable = m(..)
The hint that stems from the variable declaration may not be very useful since the variances
are not compatible. Nevertheless, it can be accepted to produce better error messages.