Fix untrusted embedding visibility in multi windowing mode

Before, we search overlay within the same root Task, which can be other
task in split. Now, we only search within the same leaf Task.

Bug: 197364677
Test: atest WmTests:TaskFragmentTest
Change-Id: I64dfdf322a15cfd80f169d0ddfc6e9bbf94d2a03
2 files changed