Turn large macros in print.c to functions

Turn large macros in print.c to functions

This is easier to read and maintain, and makes the state explicit.
It is a pure refactoring; the compiled code should be equivalent.

* src/print.c (PRINTPREPARE, PRINTFINISH): Replace with...
(struct print_context, print_prepare, print_finish): ...these new
functions and explicit state in a struct.
(Fwrite_char, write_string, Fterpri, Fprin1, Fprin1_to_string)
(Fprinc, Fprint): Adapt callers.