gdb: add type::name / type::set_name

gdb: add type::name / type::set_name

Add the `name` and `set_name` methods on `struct type`, in order to
remove the `TYPE_NAME` macro.  In this patch, the `TYPE_NAME` macro is
changed to use `type::name`, so all the call sites that are used to set
the type name are changed to use `type::set_name`.  The next patch will
remove `TYPE_NAME` completely.

gdb/ChangeLog:

	* gdbtypes.h (struct type) <name, set_name>: New methods.
	(TYPE_CODE): Use type::name.  Change all call sites used to set
	the name to use type::set_name instead.