Add formatting

[zoidyzoidzoid]

I'm quite an Elixir and VS Code noob, but would it be possible to add formatting like vscode-eex-format to ~H strings?

I'd happily help out however I can if it is possible.

[frankdugan3]

SurfaceFormatter may provide most of the heavy-lifting for this!

[pwightman]

Loving that we can now format Surface code with mix format! Any way to get VSCode to do it on save though?

[frankdugan3]

@pwightman Since ELixir now supports formatter plugins and Surface now has a compatible plugin, you can track this issue: elixir-lsp/elixir-ls#660