Consider letterbox offset as size mismatch

If there is non zero letterbox offset, that means the activity
window is not aligned with the task, then it still needs to
undo the offset to snapshot. E.g. window position is (50,0),
then the snapshot should be (-50,0) because task snapshot already
contains the offset.

Bug: 372482710
Flag: EXEMPT bugfix
Test: Set config_highResTaskSnapshotScale to 1.
      Hot launch an activity with LAYOUT_IN_DISPLAY_CUTOUT_MODE_NEVER.
      The snapshot buffer layer should align with app window.
Change-Id: I47dba6148f0c1cd610b5003f7e6fc97ae5f7404b