[Motion] Unloaded ImageView when returning from MaterialContainerTransform

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**Description:**
I'm using `MaterialContainerTransform` to transition from _Fragment A_, to a _Fragment B_ that contains a `RecyclerView` whose items have `ShapeableImageView`s. Note: _Fragment A_ is part of a `ViewPager2`, hosted by _Fragment Z_.

Transitionning from A to B works fine: transition is postponed until B's `RecyclerView` display is ready.
But when returning from B, we notice that images (that are loaded with Glide) are reset and blank.


**Expected behavior:**
Images loaded into `ImageView`s should not be reset ; those should be preserved in the return transition.
Also, why is `SheapeableImageView` showing black rounded corners ? This strange behavior of `ShapeableImageView` is also noticeable on Android Studio's layout preview (corners are then light grey).

**Source code:**

In Fragment Z:
```kotlin
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
postponeEnterTransition(1000, TimeUnit.MILLISECONDS)
// Configure ViewPager adapter...
}
```

In Fragment A:
```kotlin
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
// Some view initialization code [...]
viewModel.liveData.observe(viewLifecycleOwner) {
adapter.submitList(it)
val fragmentZ = requireParentFragment()
fragmentZ.requireView().parent?.doOnPreDraw {
fragmentZ.startPostponedEnterTransition()
}
}
}

private fun displayFragmentB() {
// Root item view from the clicked element in RecyclerView. Has transitionName set in onBindViewHolder
val itemView = ...
val sharedElementExtras = FragmentNavigatortExtras(itemView to "some_item_id")
requireParentFragment().apply {
exitTransition = Hold().apply {
duration = 300
addTarget(R.id.fragment_z)
}
// Reset transition set by other navigation events
reenterTransition = null
}

findNavController().navigate(R.id.to_fragment_b, sharedElementExtras)
}
```

In Fragment B:
```kotlin
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)

sharedElementEnterTransition = MaterialContainerTransform().apply {
drawingViewId = R.id.nav_host_fragment
duration = 300
scrimColor = Color.TRANSPARENT
setAllContainerColors(themeColorSurface)
}
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)

postponeEnterTransition(500, TimeUnit.MILLISECONDS)
view.transitionName = "some_item_id"

viewModel.liveData.observe(viewLifecycleOwner) {
adapter.submitList(it)
view.parent?.doOnPreDraw {
startPostponedEnterTransition()
}
}
}
```

**Android API version:** 29 (Q)

**Material Library version:** 1.2.1

**Device:** Nokia 7.1, but also encountered on emulator.

Start with the Fragment A, B, and Z transition snippets and reproduce the return navigation on Android API 29 using MaterialContainerTransform, RecyclerView, Glide-loaded ImageViews, and ShapeableImageView. Compare the return transition with the reported blank images and black rounded corners; done means the images remain visible and the corner rendering is explained or corrected.

Written by the indexing model from the issue text.