IR text tests: Stable blank lines between declarations in class

Rework rendering of kt-like dump and signatures dump in order to avoid
unstable blank line between declarations of the same level:
1. No blank line for the first declaration inside the member scope of
the class.
2. Always a single blank line between each two subsequent declarations
inside the member scope of the class.

compiler/testData/ir/irText/firProblems/MultiList.kt.txt

@@ -45,7 +45,6 @@ data class Some<T : Any?> {
 }
 
 interface MyList<T : Any?> : List<Some<T>> {
-
 }
 
 open class SomeList<T : Any?> : MyList<T>, ArrayList<Some<T>> {