Fix module augmentation in @parcel/transformers-typescript-types

[astegmaier]

↪️ Pull Request

Edit: This PR is ready for a review - it works to solve the issues below, and includes a unit test to cover this case.

I'd appreciate any feedback - I'm new to this part of parcel, and I want to make sure I don't break anything.

There are two issues that this PR tries to solve, both identified in #7306:

1. The current implementation of @parcel/transformer-typescript-types (intentionally) flattens all module declarations, including declarations that are intended to augment an external modules. Then, it will tree-shake things that it finds in the module augmentation, which (most of the time) will result in them being removed. This PR solves the issue by avoiding flattening "nested" module declarations - e.g. module declarations that appear within other module declarations.
2. There is a bug where if you have a module declaration in the middle of your source file, then exports declared after that declaration get (mistakenly) removed, because we think they are unused e.g.:

   import { Person } from "original";
   Person.prototype.greet = function() { return `Hello ${this.name}!` }
   // Exports declared before the augmentation declaration are present.
   export const anotherThing: string = "hello";
   
   declare module "original" {
     interface Person {
       greet(): string;
     }
   }
   // Everything after this point will be missing from the .d.ts file.
   export const somethingElse: string = "goodbye"; 

   This PR solves the issue by using a stack to keep track of what level of module declaration you are in, and making sure to associate each node with the correct module even as you visit deep nodes, and then jump back out to the original parent node.

🚨 Test instructions

See the "should work with module augmentation" test in packages/core/integration-tests/test/ts-types.js.

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs

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[devongovett]

Thank you!!