feat: unassertCode function

[RebeccaStevens]

Based off #42 (merging this will also merge that one's changes (closes #42)).

This function is designed to work on the code rather than the ast (an ast is still required in order to navigate the code).

• It returns the modified code and optionally a source map for the changes it makes.
• It will make minimal changes to the code rather than regenerated all of it from scratch using the modified ast.

I also added a large amount of JSDoc to the source code to help with typings.

[RebeccaStevens]

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