Improve location permanence in the AST

[charles-rs]

One way of doing this would be to make sure that internally, everything is constructed with a location, and also to send locations to children if they don't have them. This would lead to less "unknown location" error messages

[andrewcmyers]

I recommend having a location in the node constructors so you can't forget.

[dzagieboylo]

The main reason we don't is that the "location" information comes from the parser generator library and it is a mutable field on all AST nodes.

Adding our own location information in the constructors would be fine but it is redundant.