Android: taildrop sharing should share the `STREAM` if it exists, not the `TEXT`

### What is the issue?

Sharing a scan from within the Office Lens app to a desktop PC (i.e. macOS) shares a text file that looks like a shitty email signature ad:

```
Created by Microsoft Lens
https://go.microsoft.com/fwlink/?LinkID=524811
```

The actual shared PDF file is nowhere to be seen.

If you intercept the intent, it sends 3 extras: SUBJECT, TEXT and STREAM.
SUBJECT is the file name, TEXT is the slimy ad and STREAM is the actual file I want.

Tailscale seems to only look at the TEXT and discards the STREAM.

### Steps to reproduce

1. Scan something with Office Lens
2. Share it with Tailscale
3. Send to desktop machine

### Are there any recent changes that introduced the issue?

_No response_

### OS

Android

### OS version

12 (LineageOS 19.1)

### Tailscale version

1.33.21-t63ad49890-g80dfbd8a0c5

### Bug report

BUG-0d93653ea2c55a27683321f72b706cc1244237cf5f6a3690395398ea03dbeb8d-20221025154817Z-9df70ca9e65f8682

Start by tracing the Android share-intent handling for Office Lens, focusing on the SUBJECT, TEXT, and STREAM extras. Reproduce the share flow and verify that when STREAM exists, the desktop receives the PDF rather than the promotional text.

Written by the indexing model from the issue text.