Sets the focused TaskFragment after WCT is applied

Request focus may not work if also requesting an activity launch
in the same WCT because the launching activity is deferred to be
resumed after the WCT applied, which will replace and update the
focus again to the launching activity.

Bug: 413596444
Test: verified locally
Flag: EXEMPT bugfix
Change-Id: Ic0cb2c9ec690f0e7d2f268f7c315a8bfaacdc15c