Member predicate AliasTemplateType::getAnInstantiation

Gets an alias instantiated from this template.

For example for MyAliasTemplate<T> in the following code, the results are MyAliasTemplate<int> and MyAliasTemplate<long>:

template<typename T>
using MyAliasTemplate = ...;

MyAliasTemplate<int> instance1;

MyAliasTemplate<long> instance2;