Provide a way to restart next-ls without leaving VScode

[NobbZ]

To mitigate after a crash (see elixir-tools/next-ls#517) I have to manually close and restart VScode to restart the LSP.

There should be an easier way to restart NextLS without having to clsoe VSCode.

[mhanberg]

you can run Developer: Reload Window from the command palette and it will effectively do that.

[NobbZ]

I will try that on the next crash