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/expressions/forWithImplicitReceivers.sig.kt.txt

@@ -34,7 +34,6 @@ class IntCell {
 //   Mangled name: IReceiver
 //   Public signature: /IReceiver|null[0]
 interface IReceiver {
-
   // CHECK JVM_IR:
   //   Mangled name: IReceiver#hasNext@IntCell(){}kotlin.Boolean
   //   Public signature: /IReceiver.hasNext|8807543829800046753[0]