Update Notification.shortCriticalText doc to recommend 7 chars, not 5.

If we expect a lot of apps to put times like "10:15pm", we should recommend 7 characters.

Bug: 337261753
Change-Id: I3ea89f544628b64222bac3829752793a3a9236c0
Flag: android.app.api_rich_ongoing
Test: compiles
1 file changed