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.
Previously, creating a declaration with Fir2IrCallableDeclarationsGenerator/
Fir2IrClassifiersGenerator didn't guarantee that this declaration will
be actually added to the list of parent class/file declarations, which
lead to situations when FIR2IR created some declarations in the air
(mostly fake-overrides)