[test] Mark tests that use experimental/upcoming features as such

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.

test/SourceKit/Macros/macro_basic.swift

@@ -122,6 +122,7 @@ func remoteCall<Result: ConjureRemoteValue>(function: String, arguments: [String
 }
 
 // REQUIRES: swift_swift_parser, executable_test, shell, asserts
+// REQUIRES: swift_feature_PreambleMacros
 
 // RUN: %empty-directory(%t)