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 can't really treat them as always-initialized because that makes move checking
think that there's a value to destroy even on initialization, causing deinits to
run on uninitialized memory. Remove my previous hack, and use a `zeroInitializer`
to initialize the value state when emitting `init`, which is where we really need
the bootstrapping-into-initialized behavior. rdar://113057256
