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/declarations/contextReceivers/property.sig.kt.txt

@@ -2,7 +2,6 @@
 //   Mangled name: A
 //   Public signature: /A|null[0]
 interface A {
-
   // CHECK JVM_IR:
   //   Mangled name: A#a(){}kotlin.Int
   //   Public signature: /A.a|5993980063692763883[0]
@@ -19,7 +18,6 @@ interface A {
 //   Mangled name: B
 //   Public signature: /B|null[0]
 interface B {
-
   // CHECK JVM_IR:
   //   Mangled name: B#b(){}kotlin.Int
   //   Public signature: /B.b|-6472101675379091489[0]