Implement serde::Deserialize for sway-ast types

[camden-smallwood]

Description

This commit implements serde::Deserialize for all of the AST structures in the sway-ast crate. This would allow for deserializing from their serialized state, which would be useful for a number of different applications.

A few other small changes were necessary for this commit:

• Implements serde::Deserialize for the Ident and Span types in the sway-types crate, because they are used throughout the sway-ast crate.
• Implements Default for the ErrorEmitted trait, because it is required by serde::Deserialize.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

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[IGI-111]

This looks good overall but it is missing tests. You need to add some.