Specify the display ID to mirror for media projection

In VirtualDisplayConfig, the default value of mDisplayIdToMirror is DEFAULT_DISPLAY. In order to make media projection work for
visible background users (running on secondary displays), this CL
passed the correct display ID when building VirtualDisplayConfig.

Bug: 365184692
Test: atest CtsMediaProjectionTestCases
Test: atest --user-type secondary_user CtsMediaProjectionTestCases
Test: atest --user-type secondary_user_on_secondary_display  CtsMediaProjectionTestCases
Flag: EXEMPT bugfix
Change-Id: I9b00b80a9a69643177054e7b2248fa40ddabb448