Restore old BackstackReader.isInBackstack() implementation once AndroidX Fragment 1.2.1 is released

[lukaszkalnik]

There is a bug in AndroidX Fragment 1.2.0 which crashes the app when changing orientation in fragments or when switching fragments. This is because of our BackstackReader.isInBackstack() hacky implementation.
sockeqwe/mosby#318 (comment)

A temporary workaround has been implemented for this bug here:
#205
However, the workaround uses reflection so our previous hack for this problem has to be restored once AndroidX Fragment 1.2.1 gets released (this release will fix the current bug):
https://issuetracker.google.com/issues/148189412

[wietsebuseyne]

androidx:fragment 1.2.2 is out, so the old implementation should work again :-)
Thank you for your work BTW