Support javascriptreact and typescriptreact filetypes

[strokirk]

coc.vim and several other plugins have started to use the filetype javascriptreact for .jsx files: https://github.com/neoclide/coc.nvim/blob/master/doc/coc.txt#L945-L947

This is in order to support VS code plugins better, which seems to recommend that extension type: https://microsoft.github.io/language-server-protocol/specification

This doesn't work with Neoformat by default, but it would be great if it could. I'm not sure about the best way to approach this, otherwise I'd be glad to provide a PR.