gdb: Convert language la_printchar field to a method

This commit changes the language_data::la_printchar function pointer
member variable into a member function of language_defn.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* ada-lang.c (ada_language_data): Delete la_printchar initializer.
	(ada_language::printchar): New member function.
	* c-lang.c (c_language_data): Delete la_printchar initializer.
	(cplus_language_data): Likewise.
	(asm_language_data): Likewise.
	(minimal_language_data): Likewise.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_printchar): Rename to f_language::printchar.
	(f_language_data): Delete la_printchar initializer.
	(f_language::printchar): New member function, implementation from
	f_printchar.
	* go-lang.c (go_language_data): Delete la_printchar initializer.
	* language.c (unk_lang_printchar): Delete.
	(language_defn::printchar): Define new member function.
	(unknown_language_data): Delete la_printchar initializer.
	(unknown_language::printchar): New member function.
	(auto_language_data): Delete la_printchar initializer.
	(auto_language::printchar): New member function.
	* language.h (language_data): Delete la_printchar field.
	(language_defn::printchar): Declare new member function.
	(LA_PRINT_CHAR): Update call to printchar.
	* m2-lang.c (m2_language_data): Delete la_printchar initializer.
	(m2_language::printchar): New member function.
	* objc-lang.c (objc_language_data): Delete la_printchar
	initializer.
	* opencl-lang.c (opencl_language_data): Likewise.
	* p-lang.c (pascal_language_data): Delete la_printchar
	initializer.
	(pascal_language::printchar): New member function.
	* rust-lang.c (rust_printchar): Rename to
	rust_language::printchar.
	(rust_language_data): Delete la_printchar initializer.
	(rust_language::printchar): New member function, implementation
	from rust_printchar.