Add functions to operate on code actions based on their kind

[michaelpj]

Code actions have kinds. It seems like there's a fair bit of scope for the client to do things with code actions of a particular kind. Thoughts that occur to me:

• Apply all actions of a particular kind in a buffer/region (haskell-language-server implements a custom "Apply all hints" action that's effectively "apply all actions of kind quickfix" - we should be able to do that generically, and handle regions etc.)
• Get all actions of a particular kind and present the user with a selection menu using a custom prompt (Add interactive command for case splitting lsp-haskell#112 is essentially this)

Clients might want to implement custom functions on top of this that have meanings for particular code actions kinds that are unique to their servers, but it would be handy to have the building blocks in lsp-mode.

[nbfalcon]

Point 2 will be implemented as part of #2402.