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/external/kt38765.fir.kt.txt

@@ -55,7 +55,7 @@ open external class internal {
   }
 
   interface NestedExternalInterface {
-
   }
 
 }
+

compiler/testData/ir/irText/js/external/kt38765.kt.txt

@@ -2,6 +2,7 @@ package events
 
 open external class internal {
   external constructor() /* primary */
+
   open external class EventEmitterP : internal {
     external constructor() /* primary */
 
@@ -19,6 +20,7 @@ open external class internal {
 
   external enum class NestedExternalEnum : Enum<NestedExternalEnum> {
     private external constructor() /* primary */
+
     A = NestedExternalEnum()
 
     B = NestedExternalEnum()
@@ -33,7 +35,6 @@ open external class internal {
   }
 
   external interface NestedExternalInterface {
-
   }
 
 }

compiler/testData/ir/irText/js/external/kt38765.sig.kt.txt

@@ -37,6 +37,7 @@ open external class internal {
     //   Public signature: events/internal.NestedExternalEnum.<init>|-5645683436151566731[0]
     //   Public signature debug description: <init>(){}
     private external constructor() /* primary */
+
     // CHECK:
     //   Mangled name: events.internal.NestedExternalEnum.A
     //   Public signature: events/internal.NestedExternalEnum.A|null[0]
@@ -122,7 +123,6 @@ open external class internal {
   //   Mangled name: events.internal.NestedExternalInterface
   //   Public signature: events/internal.NestedExternalInterface|null[0]
   external interface NestedExternalInterface {
-
   }
 
   // CHECK: