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/annotations/constructorsWithAnnotations.sig.kt.txt

@@ -35,6 +35,7 @@ class TestClass {
   //   Public signature debug description: <init>(){}
   @TestAnn(x = 1)
   constructor() /* primary */
+
   // CHECK:
   //   Mangled name: TestClass#<init>(kotlin.Int){}
   //   Public signature: /TestClass.<init>|-5182794243525578284[0]