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/reflectFindAnnotationOnDefaultMethodParameter.sig.kt.txt

@@ -14,7 +14,6 @@ open annotation class Ann : Annotation {
 //   Mangled name: I
 //   Public signature: /I|null[0]
 interface I {
-
   // CHECK:
   //   Mangled name: I#m(kotlin.String){}
   //   Public signature: /I.m|934693771674457301[0]