Support for LSP/tsserver Code Actions (#3437)

* Added tsserver and LSP code action support.
* tsserver refactors support added.
* Handling special case when new text is added after new line symbol.
* ale#code_action#ApplyChanges simplified.
* Initial attempt on LSP Code Actions.
* workspace/executeCommand added.
* Some null checks added.
* Add last column to LSP Code Action message.
* Pass diagnostics to LSP code action.

Previously ApplyChanges code was applied from top-to-bottom that required 
extra parameters to track progress and there was bug. I have changed code
to bottom-to-top approach as that does not require those extra parameters
and solved the bug.

Tested with typescript-language-server and it is working.

autoload/ale/completion.vim

@@ -617,6 +617,7 @@ function! ale#completion#ParseLSPCompletions(response) abort
         let l:user_data = {'_ale_completion_item': 1}
 
         if has_key(l:item, 'additionalTextEdits')
+        \ && l:item.additionalTextEdits isnot v:null
             let l:text_changes = []
 
             for l:edit in l:item.additionalTextEdits