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/declarations/contextReceivers/compoundAssignmentOperators.sig.kt.txt

@@ -47,6 +47,7 @@ data class Result {
   //   Public signature: /Result.<init>|-5182794243525578284[0]
   //   Public signature debug description: <init>(kotlin.Int){}
   constructor(i: Int) /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: Result#component1(){}kotlin.Int
   //   Public signature: /Result.component1|-8217597213800111288[0]