introduce symbol scope, use for elixir private

fixes #225

lua/aerial/backends/treesitter/extensions.lua

@@ -72,6 +72,9 @@ M.elixir = {
     local identifier = (utils.get_at_path(match, "identifier") or {}).node
     if identifier then
       local name = vim.treesitter.query.get_node_text(identifier, bufnr) or "<parse error>"
+      if name == "defp" then
+        item.scope = "private"
+      end
       item.kind = M.elixir.kind_map[name] or item.kind
       if name == "callback" and item.parent then
         item.parent.kind = "Interface"

lua/aerial/data.lua

@@ -14,6 +14,7 @@ local config = require("aerial.config")
 ---@field parent? aerial.Symbol
 ---@field selection_range? aerial.Range
 ---@field children? aerial.Symbol[]
+---@field scope? string
 
 ---@class aerial.BufData
 ---@field bufnr integer

tests/treesitter/elixir_spec.lua

@@ -34,6 +34,7 @@ describe("treesitter elixir", function()
             kind = "Function",
             name = "private_function",
             level = 1,
+            scope = "private",
             lnum = 10,
             col = 2,
             end_lnum = 11,