gdb: Convert language la_is_string_type_p field to a method

gdb: Convert language la_is_string_type_p field to a method

This commit changes the language_data::la_is_string_type_p 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_is_string_type_p
	initializer.
	(ada_language::is_string_type_p): New member function.
	* c-lang.c (c_language_data): Delete la_is_string_type_p
	initializer.
	(cplus_language_data): Likewise.
	(asm_language_data): Likewise.
	(minimal_language_data): Likewise.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_is_string_type_p): Delete function, implementation
	moved to f_language::is_string_type_p.
	(f_language_data): Delete la_is_string_type_p initializer.
	(f_language::is_string_type_p): New member function,
	implementation from f_is_string_type_p.
	* go-lang.c (go_is_string_type_p): Delete function, implementation
	moved to go_language::is_string_type_p.
	(go_language_data): Delete la_is_string_type_p initializer.
	(go_language::is_string_type_p): New member function,
	implementation from go_is_string_type_p.
	* language.c (language_defn::is_string_type_p): Define new member
	function.
	(default_is_string_type_p): Make static, add comment copied from
	header file.
	(unknown_language_data): Delete la_is_string_type_p initializer.
	(unknown_language::is_string_type_p): New member function.
	(auto_language_data): Delete la_is_string_type_p initializer.
	(auto_language::is_string_type_p): New member function.
	* language.h (language_data): Delete la_is_string_type_p field.
	(language_defn::is_string_type_p): Declare new function.
	(default_is_string_type_p): Delete desclaration, move comment to
	definition.
	* m2-lang.c (m2_is_string_type_p): Delete function, implementation
	moved to m2_language::is_string_type_p.
	(m2_language_data): Delete la_is_string_type_p initializer.
	(m2_language::is_string_type_p): New member function,
	implementation from m2_is_string_type_p.
	* objc-lang.c (objc_language_data): Delete la_is_string_type_p
	initializer.
	* opencl-lang.c (opencl_language_data): Likewise.
	* p-lang.c (pascal_is_string_type_p): Delete function,
	implementation moved to pascal_language::is_string_type_p.
	(pascal_language_data): Delete la_is_string_type_p initializer.
	(pascal_language::is_string_type_p): New member function,
	implementation from pascal_is_string_type_p.
	* rust-lang.c (rust_is_string_type_p): Delete function,
	implementation moved to rust_language::is_string_type_p.
	(rust_language_data): Delete la_is_string_type_p initializer.
	(rust_language::is_string_type_p): New member function,
	implementation from rust_is_string_type_p.
	* valprint.c (val_print_scalar_or_string_type_p): Update call to
	is_string_type_p.