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/substitutionOverrideWithDelegate.kt.txt

@@ -34,7 +34,6 @@ open class DelegatedB : B<String> {
 }
 
 interface B<out T : Any?> : A {
-
 }
 
 class C<out T : Any?> : B<T> {