fix window insets related bugs

[connyduck]

• Fixes the background of the ComposeActivity in table mode which looked weird since Full support for Android 15, edge-to-edge mode on Android 15 #4897
• The ComposeActivity in tablet mode will now resize when the keyboard expands, the previously used fixed height would cause the bottom bar to hide entered text on some devices, closes last lines of long toot get cut off in compose toot window #4973
• The bottom sheets in the compose view will now be in fully hidden state by default, as some weirdness on some devices caused them to peek over the bottom bar in half collapsed state. Please test @fin-w
• The bottom sheet in the image viewer will now expand a bit more in edge-to-edge mode so it doesn't look it is deliberately obscured by the system bar. The image also moves up a bit so it won't be covered by the bottom sheet as much.
• The "Performing lookup…" bottom sheet won't be covered by the nav bar anymore

[fin-w]

@connyduck I can confirm this fixes my issue, many thanks!