[clangd][NFC] Simplify handing on methods with no params

Add bind methods handling the case when a method has an empty params interface and when it has no parameters.

Remove ShutdownParams and ExitParams from Protocol, In LSP they aren't defined, instead the methods are defined to have void as the params. This signature now better reflects that.

Reviewed By: sammccall

Differential Revision: https://reviews.llvm.org/D95270