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/firProblems/thisInEnumConstructor.sig.kt.txt

@@ -22,6 +22,7 @@ enum class EE : Enum<EE> {
   //   Public signature: /EE.<init>|1280618353163213788[0]
   //   Public signature debug description: <init>(kotlin.String){}
   private constructor(myName: String) /* primary */
+
   // CHECK:
   //   Mangled name: EE.ENTRY
   //   Public signature: /EE.ENTRY|null[0]