db9d0245d1
Neovim supports [commenting and uncommenting lines](https://neovim.io/doc/user/various.html#commenting) based on what the 'commentstring' option is set to, but this isn't set for TableGen files. The filetype plugin for C++ built into both vim and neovim sets 'commentstring' to `// %s`, so use that in the TableGen filetype plugin as well.