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/singletons/enumEntry.sig.kt.txt

@@ -7,6 +7,7 @@ open enum class Z : Enum<Z> {
   //   Public signature: /Z.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   private constructor() /* primary */
+
   // CHECK:
   //   Mangled name: Z.ENTRY
   //   Public signature: /Z.ENTRY|null[0]
@@ -39,6 +40,7 @@ open enum class Z : Enum<Z> {
     //   Public signature: /Z.ENTRY.<EEC>.<init>|-5645683436151566731[0]
     //   Public signature debug description: <init>(){}
     private constructor() /* primary */
+
     // CHECK JVM_IR:
     //   Mangled name: Z.ENTRY#compareTo(Z){}kotlin.Int
     //   Public signature: /Z.ENTRY.<EEC>.compareTo|-7935111597565816011[0]