gdb: Convert language la_watch_location_expression field to a method

gdb: Convert language la_watch_location_expression field to a method

This commit changes the language_data::la_watch_location_expression
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_watch_location_expression): Rename to
	ada_language::watch_location_expression.
	(ada_language_data): Delete la_watch_location_expression
	initializer.
	(ada_language::watch_location_expression): New member function,
	implementation from ada_watch_location_expression.
	* breakpoint.c (watch_command_1): Update call to
	watch_location_expression.
	* c-lang.c (c_watch_location_expression): Rename to
	language_defn::watch_location_expression.
	(c_language_data): Delete la_watch_location_expression
	initializer.
	(cplus_language_data): Likewise.
	(asm_language_data): Likewise.
	(minimal_language_data): Likewise.
	* c-lang.h (c_watch_location_expression): Delete declaration.
	* d-lang.c (d_language_data): Delete la_watch_location_expression
	initializer.
	* f-lang.c (f_language_data): Likewise.
	* go-lang.c (go_language_data): Likewise.
	* language.c (language_defn::watch_location_expression): Member
	function implementation from c_watch_location_expression.
	(unknown_language_data): Delete la_watch_location_expression
	initializer.
	(auto_language_data): Likewise.
	* language.h (language_data): Delete la_watch_location_expression
	field.
	(language_defn::watch_location_expression): Declare new member
	function.
	* m2-lang.c (m2_language_data): Delete
	la_watch_location_expression 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_watch_location_expression): Rename to
	rust_language::watch_location_expression.
	(rust_language_data): Delete la_watch_location_expression
	initializer.
	(rust_language::watch_location_expression): New member function,
	implementation from rust_watch_location_expression.