If, as PR 10368 suggests, more parameters should be added to `getViewport` I think that it would be a mistake to not change the signature *first* to avoid needlessly unwieldy call-sites.
To not break any existing code and third-party use-cases, this is obviously implemented with a deprecation warning *and* with a working fallback[1] for the old method signature.
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[1] This is limited to `GENERIC` builds, which should be sufficient.
This patch lets the AcroForms example make use of the built-in interactive
forms functionality in PDF.js. This makes the example:
- much easier to understand;
- more feature-complete;
- in sync with the core when new functionality is added;
- similar to the other examples in terms of structure.
