Restore Recents TaskView based on all taskIDs, not first

* Return a copy of taskIds in TaskView#getTaskIds() to
prevent accessors from getting clobbered values
* In RecentsView#applyLoadPlan we overwrite values in that
array, so callers using it to cache old values would read
incorrect values when reading it after a TaskView has been
bound to new tasks.
* Load/Unload visible task data for all tasks in a given
TaskView, not just single task <-- probably not necessary for
bug fix, but seems sensible

Flag: none
Fixes: 266905177
Test: Quickswitch works as expected. Currently
unable to test thumbnails (created b/281582106)
Change-Id: Ifd4d8a856976ab9cc200b0f61eca1c68897f343c