Feat: Configure discussion tree split width and position

This MR improves the configurability of the plugin by using Nui's split
system rather than managing the splits ourselves. This lets the user
configure both the positioning of the discussion tree and it's width,
and reduces overall maintenance of split management for the plugin.

lua/gitlab/discussions.lua

@@ -1,5 +1,6 @@
 local u            = require("gitlab.utils")
 local NuiTree      = require("nui.tree")
+local NuiSplit     = require("nui.split")
 local job          = require("gitlab.job")
 local state        = require("gitlab.state")
 local Job          = require("plenary.job")
@@ -57,11 +58,12 @@ M.list_discussions = function()
             return
           end
 
-          vim.cmd.tabnew()
-          local buf = vim.api.nvim_create_buf(false, true)
-          vim.api.nvim_command("aboveleft vsplit")
-          vim.api.nvim_buf_set_option(buf, 'filetype', 'markdown')
-          vim.api.nvim_set_current_buf(buf)
+          local splitState = state.DISCUSSION_SPLIT
+          splitState.buf_options = { modifiable = false }
+          local split = NuiSplit(splitState)
+          split:mount()
+
+          local buf = split.bufnr
           local allDiscussions = {}
           for i, discussion in ipairs(data.discussions) do
             local discussionChildren = {}
@@ -90,7 +92,6 @@ M.list_discussions = function()
           state.tree:render()
           vim.api.nvim_buf_set_option(buf, 'filetype', 'markdown')
           u.darken_metadata(buf, '')
-          M.jump_to_file()
         end)
       end
     end,
@@ -105,6 +106,14 @@ M.jump_to_file     = function()
   local node = state.tree:get_node()
   if node == nil then return end
 
+  local wins = vim.api.nvim_list_wins()
+  local discussion_win = vim.api.nvim_get_current_win()
+  for _, winId in ipairs(wins) do
+    if winId ~= discussion_win then
+      vim.api.nvim_set_current_win(winId)
+    end
+  end
+
   local childrenIds = node:get_child_ids()
   -- We have selected a note node
   if node.file_name ~= nil then