[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/SILGen/inlinable_attribute.swift

@@ -1,5 +1,7 @@
 // RUN: %target-swift-emit-silgen -enable-experimental-feature IsolatedDeinit -module-name inlinable_attribute -emit-verbose-sil -warnings-as-errors -target %target-swift-5.1-abi-triple %s | %FileCheck %s
 
+// REQUIRES: swift_feature_IsolatedDeinit
+
 // CHECK-LABEL: sil [serialized] [ossa] @$s19inlinable_attribute15fragileFunctionyyF : $@convention(thin) () -> ()
 @inlinable public func fragileFunction() {