RangeEquals doesn't support literal std::initializer_list

[stk-ableton]

It would often be useful to write something like this:

  const auto v = calculateSomeVectorOfInts();
  CHECK_THAT(v, RangeEquals({1, 2, 3}));

This doesn't compile. It can be made to compile by adding an overload to RangeEquals that takes a std::initializer_list. Would a PR adding such an overload have a chance of being accepted?

It's not a huge issue since there are workarounds, including any of these:

  const auto expected = {1, 2, 3};
  CHECK_THAT(v, RangeEquals(expected));

  CHECK_THAT(v, RangeEquals(std::vector{1, 2, 3}));

  CHECK_THAT(v, RangeEquals(std::initializer_list<int>{1, 2, 3}));

Still, the convenience of writing the initializer_list inline without extra qualification would be nice.