Conditional OpenOp / CloseOp

In `ktfmt`, I'd like to format the following:

```
fun longName() = coroutineScope {
foo()
//
}
```

but if it doesn't fit in a single line, I'd like to get

```
fun longName() =
coroutineScope {
foo()
//
}
```

I only managed to create the first form by _not_ wrapping the lambda in an `OpenOp` / `CloseOp` block, while the second form arises naturally from such a block around `coroutine { … }`.

One way to solve this is to create a conditional `OpenOp` / `CloseOp`, similarly to `Indent.If`, and then emit a block that materializes only if there had been a break after the `=`.

What do you think?

(I admit this isn't super clear, let me know if I should make another attempt at explaining this)

cc @cushon @bethcutler

Comece rastreando o tratamento de OpenOp e CloseOp pelo formatter e, em seguida, compare-o com Indent.If. Reproduza o exemplo de coroutineScope e determine como as quebras de linha após o sinal de igual afetam a indentação. O trabalho estará concluído quando tanto a forma compacta quanto a forma com quebra de linha forem produzidas corretamente, com testes cobrindo esse comportamento.

Escrita pelo modelo de indexação a partir do texto da issue.