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/lambdas/destructuringInLambda.sig.kt.txt

@@ -57,6 +57,7 @@ data class A {
   //   Public signature: /A.<init>|-7691762014320324121[0]
   //   Public signature debug description: <init>(kotlin.Int;kotlin.Int){}
   constructor(x: Int, y: Int) /* primary */
+
   // CHECK JVM_IR:
   //   Mangled name: A#component1(){}kotlin.Int
   //   Public signature: /A.component1|-8217597213800111288[0]

compiler/testData/ir/irText/lambdas/multipleImplicitReceivers.sig.kt.txt

@@ -2,7 +2,6 @@
 //   Mangled name: IFoo
 //   Public signature: /IFoo|null[0]
 interface IFoo {
-
   // CHECK:
   //   Mangled name: IFoo@A{}foo
   //   Public signature: /IFoo.foo|1214000299789500455[0]
@@ -24,7 +23,6 @@ interface IFoo {
 //   Mangled name: IInvoke
 //   Public signature: /IInvoke|null[0]
 interface IInvoke {
-
   // CHECK JVM_IR:
   //   Mangled name: IInvoke#invoke@B(){}kotlin.Int
   //   Public signature: /IInvoke.invoke|7560171197904259096[0]