Properly newline expressions in the pretty printer

[janmasrovira]

follow-up to #1577

I think it still uses too much horizontal space and it should be improved. Also, it only works for regular application. Infix chains are treated as before.

[mariari]

follow-up to #1577

A very easy way is to maybe just newline after the := and indent by 2, so that the space up to the next line isn't 20 spaces off. (A group can be had here to optionally newline if it gets big to preserve the same like := for small expressions

[janmasrovira]

follow-up to #1577

A very easy way is to maybe just newline after the := and indent by 2, so that the space up to the next line isn't 20 spaces off. (A group can be had here to optionally newline if it gets big to preserve the same like := for small expressions

I actually tried to do that but I didn't succeed. I'll need to spend some more time with it

[janmasrovira]

This pr now includes:

1. A new data type (Ape) that represents abstract expressions to be pretty printed. They should be generic enough to be used as the backend for Concrete, Abstract and Internal. Currently only Concrete uses them.
2. A sensible algorithm for pretty printing Apes. This algorithm takes into account chains of applications or infix operators of the same fixity.
3. This new algorithm is not the default but can be disabled using the global --no-format option.
4. A new juvix-mode command: juvix-format-buffer that formats the current buffer.

I started to work on an enchancement to the algorithm that supports cycling nesting levels when the nesting level comes too close to the end of the page. However, it required a bigger refactor and it will be merged (in case we want it) in another pr. Some wip is fond in https://github.com/anoma/juvix/tree/anchor-experiment branch