librz/cons/* (TUI library/) - remove global state

[ghost]

Remove global variables

librz/cons/input.c

#define I rz_cons_singleton()

Additional context

Also related: #985

[XVilka]

I don't think we need to use any external library. So far, Rizin's own is battle tested across different systems and environments, and much smaller than alternatives. We don't require all features of the "bigger" libraries, thus I think it's better to keep it.

[ret2libc]

That said, it would definitely benefit from more unit tests and better API, as all the other librz modules :(