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/delegatedImplementationWithExplicitOverride.sig.kt.txt

@@ -7,6 +7,7 @@ class C : IFooBar {
   //   Public signature: /C.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   constructor() /* primary */
+
   // CHECK:
   //   Mangled name: C#foo(){}
   //   Public signature: /C.foo|-1041209573719867811[0]
@@ -25,7 +26,6 @@ class C : IFooBar {
 //   Mangled name: IFooBar
 //   Public signature: /IFooBar|null[0]
 interface IFooBar {
-
   // CHECK:
   //   Mangled name: IFooBar#bar(){}
   //   Public signature: /IFooBar.bar|496682602797471549[0]