insert/replace completion support

LSP protocol describes two types of completion: insert, and replace.
It turns out its really easy to support this. The hard part is just
checking if the client actually wants it.

src/fennel-ls/completion.fnl

@@ -136,7 +136,11 @@ is set to true and we report that we support completionItem/resolve."
           (expression-completions)))
 
     (if server.can-do-good-completions?
-      {:itemDefaults {:editRange range :data {: uri : byte}}
+      {:itemDefaults {:editRange (if server.can-do-insert-replace-completions?
+                                     {:insert {:start range.start :end position}
+                                      :replace range}
+                                     range)
+                      :data {: uri : byte}}
        :items results}
       results)))
 

src/fennel-ls/config.fnl

@@ -132,6 +132,7 @@ However, when not an option, fennel-ls will fall back to positionEncoding=\"utf-
        (case (?. params :capabilities :textDocument :completion :completionList :itemDefaults)
           completion-item-defaults  (and (accumulate [found nil _ v (ipairs completion-item-defaults) &until found] (= v :editRange))
                                          (accumulate [found nil _ v (ipairs completion-item-defaults) &until found] (= v :data)))))
+  (set server.can-do-insert-replace-completions? (?. params :capabilities :textDocument :completion :completionItem :insertReplaceSupport))
   (reload server))
 
 {: initialize