LibWeb+LibGC: Import GC swift module into LibWeb and an initial user

Start work on a speculative HTML Parser in Swift. This component will
walk ahead of the normal HTML parser looking for fetch() requests to
make while the normal parser is blocked. This work exposed many holes in
the Swift C++ interop component, which have been reported upstream.

Libraries/LibWeb/Loader/FileRequest.h

@@ -9,6 +9,7 @@
 #include <AK/ByteString.h>
 #include <AK/Error.h>
 #include <AK/Function.h>
+#include <AK/Swift.h>
 
 namespace Web {
 
@@ -22,6 +23,6 @@ public:
 
 private:
     ByteString m_path {};
-};
+} SWIFT_UNSAFE_REFERENCE; // FIXME: This type is actually move-only, not unsafe
 
 }