feat: format

[a-frantz]

Describe the problem or feature in addition to a link to the issues.

New crate, wdl-format! Handles all things formatting!

In the interest of keeping this PR from sprawling further, there are some known issues/TODOs that will be handled in follow-up PRs.

1. Right now, every Expr is just copied verbatim instead of being actually formatted. Actually formatted them in all their complexity will involve a lot of new code.
2. Placeholders in literal strings are similarly copied verbatim, but will be formatted in a follow-up
3. Whitespace is always ignored in the current PR. A future PR will implement respecting certain line-breaks and blank lines.
4. Sorting input sections

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