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/js/native/nativeNativeKotlin.kt.txt

@@ -2,12 +2,14 @@ package foo
 
 open external class A {
   external constructor() /* primary */
+
   external fun foo(): String
 
 }
 
 open external class B : A {
   external constructor() /* primary */
+
   external fun bar(): String
 
 }

compiler/testData/ir/irText/js/native/nativeNativeKotlin.sig.kt.txt

@@ -51,6 +51,7 @@ class C : B {
   //   Public signature: foo/C.<init>|-5645683436151566731[0]
   //   Public signature debug description: <init>(){}
   constructor() /* primary */
+
   // CHECK JS_IR NATIVE:
   //   Mangled name: foo.C#bar(){}
   //   Public signature: foo/C.bar|496682602797471549[0]