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/DeepCopyIrTree.kt.txt

@@ -1,5 +1,4 @@
 interface IrType {
-
 }
 
 interface TypeRemapper {
@@ -19,7 +18,6 @@ interface IrTypeParametersContainer : IrDeclaration, IrDeclarationParent {
 }
 
 interface IrDeclaration {
-
 }
 
 interface IrTypeParameter : IrDeclaration {
@@ -29,7 +27,6 @@ interface IrTypeParameter : IrDeclaration {
 }
 
 interface IrDeclarationParent {
-
 }
 
 class DeepCopyIrTreeWithSymbols {