SplitPane by design, shouldn't have default visual representation, because it mostly depends on the design system (material, material3, etc)
Fixes https://github.com/JetBrains/compose-jb/issues/1975
RelNote:
SplitPane no longer depends on compose.material. Now, by default, SplitPane has invisible 0px splitter, not 1px black/white splitter as it was before. If you want to preserve the previous behaviour, specify a splitter explicitly:
```
HorizontalSplitPane(splitterState) {
splitter {
visiblePart {
Box(
Modifier
.height(1.dp)
.fillMaxHeight()
.background(MaterialTheme.colors.background)
)
}
}
}
```
