[Swift] Add documentation to input structs' init

[kevinmbeaulieu]

Implement feature request to add documentation to input structs' generated constructors.

Generates documentation of the form:

/// - Parameters:
///   - someUndocumentedField
///   - someDocumentedField: This field has a documentation comment. When it is really long,
/// it wraps like this.

The way the text wraps is admittedly not ideal, but I couldn't think of a good way to make it wrap like this:

///   - someDocumentedField: This field has a documentation comment. When it is really long,
///                          it would be nice if it wrapped like this.

TODO:

• Update CHANGELOG.md* with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[zionts]

@designatednerd you might be the right person to take a look here :)

[designatednerd]

Ooh neat! Sorry I missed this when it was submitted!

[kevinmbeaulieu]

No prob, thanks! Just rebased so should be safe for someone to merge once CI finishes re-running