Send to the conversation picked in the share sheet

[Xant3s]

Content

The Direct Share row of the system share sheet already offered conversations, but picking one did nothing with that choice: the app still showed the account picker (when there is more than one account), then the room picker. The system names the chosen shortcut in Intent.EXTRA_SHORTCUT_ID, which nothing read. The share now carries that id, and the session it belongs to resolves the room it was built for.

Follows #7574, which declared the <share-target> that makes the row appear.

Motivation and context

Part of #3835

Tests

Unit tests cover the id format (ConversationShortcutIdTest), the id reaching ShareIntentData for both plain text and uris (DefaultShareIntentHandlerTest), and the presenter sending without a selection — including the case where the shortcut belongs to a different account than the one handling the share (SharePresenterTest).

Manually:

• Send a message in a room, so its conversation shortcut is published.
• Share text from another app and pick that conversation in the Direct Share row.
  The message is sent to that room, with no account or room picker.
• Same with an image.

Tested devices

• Physical
• Emulator
• OS version(s): API 34 (Android 14)

Checklist

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• Changes have been tested on an Android device or Android emulator with API 24
• UI change has been tested on both light and dark themes
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• Pull request title will be used in the release note, it clearly defines what will change for the user
• Pull request includes screenshots or videos if containing UI changes
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