Add XFA support to AcroForm module

[dsolankii]

Summary

• add addXFA entry point to embed XFA payloads and toggle NeedRendering
• normalize stream/array inputs, emit XFA packets during document build, and keep AcroForm fallbacks intact
• add regression coverage and extend TypeScript typings for the new API

Testing

• npm run build
• npm run test-unit
• npm run test-node
• npm run test-amd
• npm run test-esm
• npm run test-globals
• npm run test-typescript
• npm run test-webworker

Closes #3886

(Friendly note: I’m participating in Hacktoberfest—thanks for tagging or merging!)