HLS statically advertises support for functionality that is disabled by config

For example: if the semantic tokens plugin is disabled, we still see we have a plugin that provides handlers for the semantic tokens methods and so say we support it (https://github.com/haskell/haskell-language-server/issues/4081).

Probably the "correct" thing to do would be to not statically advertise support and instead dynamically register for it when the plugin is turned on. Similarly we ought to unregister if the plugin is turned off...

This would be pretty complicated to arrange, however, and is quite different from what we do today.