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/stubs/javaInnerClass.sig.kt.txt

@@ -18,6 +18,7 @@ class Test1 : J {
   //   Public signature: /Test1.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   constructor() /* primary */
+
   // CHECK:
   //   Mangled name: Test1#bar(){}
   //   Public signature: /Test1.bar|496682602797471549[0]