Use ppx_deriving.show for AST pretty-printers from lib_scoru_wasm/test/ast_printer

Context

This MR replaces hand-made pretty printers with derived ones. Note that this approach only works for non-lazy datastructures so this MR only addresses the non-lazy datastructures in lib_webassembly.

This MR partially addresses #3456

Manually testing the MR

If the project builds successfully then the derived pretty printers are good.

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR