Use private Composable functions where possible
The following discussion from !165 (merged) should be addressed:
Hmm, I guess [having private Composable functions has] been possible all the time, we just haven't made use of it the way one usually would. For example looking at
PrivateMessageScreen, all methods except
PrivateMessageScreen()could be private. I think that's pretty common in our codebase. I think we didn't stumble upon it as IntelliJ doesn't warn about @Composable functions that could be private like it does with regular methods that could be private.