Update string for message of DirectBootWarnDialog

Some users feedback to us that they are not very clear of the
meaning of the string 'direct_boot_unaware_dialog_message'.
The updated one may be more clear.

Bug: https://partnerissuetracker.corp.google.com/u/0/issues/72197006


Test: manual test. Go to the Available virtual keyboard interface,
turn on a 3rd party ime keyboard and check the message.

Change-Id: Ib3a999601fa40f678956550d8941b7cb1db8a9af
Signed-off-by: tiansiming [田思明] <tiansiming@xiaomi.com>