feat: Enables payment sharing via intents (text / image)

[tzarebczan]

Motivation: I got tired of having to take a screenshot, then having to manually open Zodl, go to send, select image, and navigate to the screenshot.

This PR adds the ability to share payment requests via SEND intents which make the app a sharable target, including text (e.g. a zcash address, or zcash: uri and images containing QR codes.

This still maintains the third-party app detection for VIEW intents.

Tried looking at adding some tests, but the new code reuses existing scan/ZIP‑321/address validators and that there were no existing tests for those paths to update. I can follow up with another attempt should it be required.

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[tzarebczan]

Rebased my PR on master, would be awesome to still get this feature in. Would enable much easier ingestion of QR/shared addresses/payment links.

[tzarebczan]

Any interest in this feature? Should be fairly safe and would be a great UX improvement around payments.

Happy to rebase and fix any issues based on feedback.

[tzarebczan]

Force pushed up the rebase, will check again after Ironwood stuff clears out - best of luck!