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/primaryConstructorWithSuperConstructorCall.sig.kt.txt

@@ -73,6 +73,7 @@ class TestWithDelegatingConstructor : Base {
   //   Public signature: /TestWithDelegatingConstructor.<init>|-5182794243525578284[0]
   //   Public signature debug description: <init>(kotlin.Int){}
   constructor(x: Int)
+
   // CHECK:
   //   Mangled name: TestWithDelegatingConstructor#<init>(kotlin.Int;kotlin.Int){}
   //   Public signature: /TestWithDelegatingConstructor.<init>|-7691762014320324121[0]