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/fromKEEP/compareTo.sig.kt.txt

@@ -37,6 +37,7 @@ data class Pair<A : Any?, B : Any?> {
   //   Public signature: /Pair.<init>|3086114026882374588[0]
   //   Public signature debug description: <init>(1:0;1:1){}
   constructor(first: A, second: B) /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: Pair#component1(){}1:0
   //   Public signature: /Pair.component1|2393470133763651536[0]