gdb: Convert language la_iterate_over_symbols field to a method

gdb: Convert language la_iterate_over_symbols field to a method

This commit changes the language_data::la_iterate_over_symbols
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_add_all_symbols): Update comment.
	(ada_iterate_over_symbols): Delete, move implementation to...
	(ada_language::iterate_over_symbols): ...here, a new member
	function, rewrite to use range based for loop.
	(ada_language_data): Delete la_iterate_over_symbols initializer.
	* c-lang.c (c_language_data): Likewise.
	(cplus_language_data): Likewise.
	(asm_language_data): Likewise.
	(minimal_language_data): Likewise.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_language_data): Likewise.
	* go-lang.c (go_language_data): Likewise.
	* language.c (unknown_language_data): Likewise.
	(auto_language_data): Likewise.
	* language.h (language_data): Delete la_iterate_over_symbols field.
	(language_defn::iterate_over_symbols): New member function.
	(LA_ITERATE_OVER_SYMBOLS): Update.
	* linespec.c (iterate_over_all_matching_symtabs): Update.
	* m2-lang.c (m2_language_data): Delete la_iterate_over_symbols
	initializer.
	* objc-lang.c (objc_language_data): Likewise.
	* opencl-lang.c (opencl_language_data): Likewise.
	* p-lang.c (pascal_language_data): Likewise.
	* rust-lang.c (rust_language_data): Likewise.