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/classes/dataClasses/kt31649.sig.kt.txt

@@ -22,6 +22,7 @@ data class TestData {
   //   Public signature: /TestData.<init>|-7885966204384349687[0]
   //   Public signature debug description: <init>(kotlin.Nothing?){}
   constructor(nn: Nothing?) /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: TestData#component1(){}kotlin.Nothing?
   //   Public signature: /TestData.component1|137173073680766068[0]
@@ -98,6 +99,7 @@ value class TestInline {
   //   Public signature: /TestInline.<init>|-7885966204384349687[0]
   //   Public signature debug description: <init>(kotlin.Nothing?){}
   constructor(nn: Nothing?) /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: TestInline#equals(kotlin.Any?){}kotlin.Boolean
   //   Public signature: /TestInline.equals|722809408929142791[0]