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/dataObject.sig.kt.txt

@@ -7,6 +7,7 @@ data object DataObject {
   //   Public signature: /DataObject.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   private constructor() /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: DataObject#equals(kotlin.Any?){}kotlin.Boolean
   //   Public signature: /DataObject.equals|722809408929142791[0]