Fetch context URL from the top-most app, send with share if available.

- Add contextUrl to ScreenshotData.
- Fork AssistContentRequester from launcher, adapt slightly for sysui
  dagger.
- Request the assist content (async) if the task ID is available.
- Set the URL as EXTRA_TEXT if available. Don't set the subject in the
  share if we have EXTRA_TEXT, as they seem to conflict with each other
  in some apps.
- Slight refactor in ActionIntentCreator to make the various ways to
  create share intents clearer.

Flag: All code changes (beyond variable existence) are protected by the
      SCREENSHOT_METADATA flag, currently disabled. The work profile
      screenshots flag is also required for this to work properly (in
      teamfood).
Bug: 242791070
Test: atest com.android.systemui.screenshot
Test: Verify that context URL from chrome passes all the way through
      when sharing with Gmail.
Change-Id: I39c3503147631f4ef79088f23c201bbad7405d16