fix: use higher-level API to get capture names

The recent breaking change of capture-based Treesitter highlight groups
[0] removed the `_get_hl_from_capture` method available on
`TSHighlighterQuery`. `get_captures_at_position` should be used instead.
The highlight group name is the capture name prefixed by the `@` symbol.

This fixes the plugin on Neovim nightly while preserving old
functionality on older versions when `get_captures_at_position` is not
available.

[0]: neovim/neovim#14090 (comment)

Author: Gelio

lua/dim.lua

@@ -77,6 +77,14 @@ end
 function util.get_treesitter_hl(row, col)
   local buf = vim.api.nvim_get_current_buf()
 
+  -- NOTE: use new functionality from https://github.com/neovim/neovim/issues/14090#issuecomment-1228444035
+  if vim.treesitter.get_captures_at_position ~= nil then
+    local matches = vim.treesitter.get_captures_at_position(buf, row, col)
+    return vim.tbl_map(function(match)
+      return "@" .. match.capture
+    end, matches)
+  end
+
   local self = highlighter.active[buf]
   if not self then
     return {}