Add DeviceConfigurationOverride for insets to allow screenshot testing insets

[alexvanyo]

This adds a way to test for #1295, by creating a DeviceConfigurationOverride.WindowInsets that allows injecting arbitrary window insets for content under test.

By using this override in host-side screenshot tests to inject a non-zero amount of system bar insets on all sides, we can visually show how the snackbar is not being inset properly, and can be obscured by the system insets.

This is a prototype for the upstream request for a DeviceConfigurationOverride.WindowInsets: https://issuetracker.google.com/343474632

[github-actions]

Combined test coverage report

Overall Project	41.4%	🍏

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[github-actions]

Combined test coverage report

Overall Project	41.37%	🍏

There is no coverage information present for the Files changed

[github-actions]

Combined test coverage report

Overall Project	41.4%	🍏

There is no coverage information present for the Files changed

[Jaehwa-Noh]

I have a question.
I used WindowInsets.safeDrawing.getBottom to avoid the System UI in
https://github.com/android/nowinandroid/pull/1296/files#diff-3fcb081475d70c62cae861a437429902dd21cd40067b7b52ec0c9c5184a1bf06R90-R95

val density = LocalDensity.current
val bottomSystemUiHeight = density.run {
WindowInsets.safeDrawing
.getBottom(density = density)
.toDp()
}

If I set the windowInsets like yours to test, the windowInsets would be set to the safeDrawing?
Is there any way to set SafeDrawing manually?

---

Aha, I found the code you set the navigation insets.
https://github.com/android/nowinandroid/pull/1498/files#diff-b76aa2071cc8cc921b26f6a03e5c8679ca440ea7b1950fecfe58f57d6abeaa3aR253-R260

.setInsets(
WindowInsetsCompat.Type.navigationBars(),
DpRect(
left = 64.dp,
top = 0.dp,
right = 64.dp,
bottom = 64.dp,
).toInsets(),