treesitter: refactor and use lua regexes

runtime/lua/vim/treesitter/language.lua

@@ -0,0 +1,26 @@
+local a = vim.api
+
+local M = {}
+
+function M.require_language(lang, path)
+  if vim._ts_has_language(lang) then
+    return true
+  end
+  if path == nil then
+    local fname = 'parser/' .. lang .. '.*'
+    local paths = a.nvim_get_runtime_file(fname, false)
+    if #paths == 0 then
+      -- TODO(bfredl): help tag?
+      error("no parser for '"..lang.."' language")
+    end
+    path = paths[1]
+  end
+  vim._ts_add_language(path, lang)
+end
+
+function M.inspect_language(lang)
+  M.require_language(lang)
+  return vim._ts_inspect_language(lang)
+end
+
+return M