This never belonged in ActorIsolationRequest since it fits perfectly in the
attribute checker. This also simplifies the logic before I add code to
getIsolationFromAttribute to handle ExecutionAttribute.
While doing #76740 I iteratively was adding new `REQUIRES:` as new
usages of the features were found, but I did not realize that at the
same time other people might be removing some of those usages. The tests
in this commit had some `REQUIRES:` line for a previous
`-enable-experimental/upcoming-feature`, but they not longer use those
features, so the `REQUIRES:` were effectively disabling the tests (at
least in the case of `KeyPathWithStaticMembers`. In other cases they
might still had executed).
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.
Instead, use the `%target-swift-5.1-abi-triple` substitution to compile the tests
for deployment to the minimum OS versions required for use of _Concurrency APIs.
