Find all the usages of `--enable-experimental-feature` or
`--enable-upcoming-feature` in the tests and replace some of the
`REQUIRES: asserts` to use `REQUIRES: swift-feature-Foo` instead, which
should correctly apply to depending on the asserts/noasserts mode of the
toolchain for each feature.
Remove some comments that talked about enabling asserts since they don't
apply anymore (but I might had miss some).
All this was done with an automated script, so some formatting weirdness
might happen, but I hope I fixed most of those.
There might be some tests that were `REQUIRES: asserts` that might run
in `noasserts` toolchains now. This will normally be because their
feature went from experimental to upcoming/base and the tests were not
updated.
We want that (repeat each Element).[P]A == (repeat (each Element).[P]A),
where on the left is type witness projection from the tuple conformance,
and on the right is a tuple with a pack expansion.
The progress on variadic generics means we can now implement useful
witnesses in a tuple conformance. The feature remains very incomplete
though, today we crash in SILGen.
