Add ui-backhandler dependency shortcut

[MaximPestryakov]

In 1.8.0 release multiplatform BackHandler and PredictiveBackHandler were implemented. But shortcut for ui-backhandler dependency wasn't. To be able to use
BackHandler you have to manually add org.jetbrains.compose.ui:ui-backhandler dependency.

Now you add the dependency like this:

dependencies {
    implementation(compose.uiBackHandler)
}