expose wdl-format in wdl-lint

[a-frantz]

this is a parent issue for #379 and #380

The primary goal for this is to expose better fix messages by formatting the relevant AST nodes and outputting them in lint diagnostics. A secondary perk is that we may be able to format a node and compare it to the input node and detect possible issues that should be reported that way.

As part of this, the wdl-format API probably needs to be modified. The current implementation lends itself to only formatting specific nodes and their children in the AST, but that isn't really exposed, as so far we've only been concerned with formatting entire documents.

This is blocked for now. A higher priority is exposing wdl-analysis in wdl-lint (issue #273 and PR #341 )