Phoenix Router with auto-alias

### Precheck

> Do a quick search and make sure the issue has not yet been reported

I did do a quick search for "router" and "route" in both open and closed issues.

### Environment

N/A since this is an observed behaviour based off of forum feedback.

### Current behavior

Hello ElixirLS team! ❤️

You are probably well aware of this but I couldn't find a logged issue so I'm opening one up.

See [here](https://elixirforum.com/t/issues-while-adding-hello-messenger-router/59333) for the latest example. If required, I can dig up two other recent discussions I was involved in where newcommers had the same issue (I did a search to find them but apparently I talk too much on that site).

### Expected behavior

I don't particularly think this is ElixirLS' fault but I still wanted to log it.

The expected behaviour would be to expand a macro to see what it does before inserting an alias. I can't say if that is unreasonable or not as I know nothing about language servers. I don't even know if anything can be done, I just wanted to log it!

Thank you for all your work! ❤️