added: lsp-haskell-execute-code-action-add-signature

[ncaq]

I want it to be a stand-alone function because I often do this in Haskell code actions.

I update Package-Requires emacs 24.3 -> 26.1, because seq-find require Emacs 25, lsp-mode of base package require 26.1, Since lsp-haskell will never work without lsp-mode, there is no point in lsp-haskell supporting old Emacs that lsp-mode does not support.

[Anton-Latukha]

Seems everything in the thread was addressed. Love providing type signatures for local functions, this would help type programming immensely.