gdb: Convert language la_collect_symbol_completion_matches field to a method

gdb: Convert language la_collect_symbol_completion_matches field to a method

This commit changes the
language_data::la_collect_symbol_completion_matches 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_collect_symbol_completion_matches): Rename to
	ada_language::collect_symbol_completion_matches.
	(ada_language_data): Delete la_collect_symbol_completion_matches
	initializer.
	(ada_language::collect_symbol_completion_matches): New member
	function, implementation from
	ada_collect_symbol_completion_matches.
	* c-lang.c (c_language_data): Delete
	la_collect_symbol_completion_matches initializer.
	(cplus_language_data): Likewise.
	(asm_language_data): Likewise.
	(minimal_language_data): Likewise.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_collect_symbol_completion_matches): Rename to
	f_language::collect_symbol_completion_matches.
	(f_language_data): Delete la_collect_symbol_completion_matches
	initializer.
	(f_language::collect_symbol_completion_matches) New member
	function, implementation from f_collect_symbol_completion_matches.
	* go-lang.c (go_language_data): Delete
	la_collect_symbol_completion_matches initializer.
	* language.c (unknown_language_data): Likewise.
	(auto_language_data): Likewise.
	* language.h (language_data): Delete
	la_collect_symbol_completion_matches field.
	(language_defn::collect_symbol_completion_matches): New member
	function.
	* m2-lang.c (m2_language_data): Delete
	la_collect_symbol_completion_matches 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.
	* symtab.c (default_collect_symbol_completion_matches): Delete.
	(collect_symbol_completion_matches): Update call to
	collect_symbol_completion_matches.
	(collect_symbol_completion_matches_type): Likewise.
	* symtab.h (default_collect_symbol_completion_matches): Delete
	declaration.