The SYM_METHOD kind of symbol was already present but never used so it
just found its purpose.

They appear in their dedicated symbol table:

    /*
     * Symbol Table MAIN
     *
     * reserved  VOID       41 41 acl
     * reserved  VOID       41 41 backend
     * [...]
     */

    /*
     * Symbol Table TYPE
     *
     * none      VOID     40 41 BACKEND
     * method    BACKEND  40 41 BACKEND.resolve
     * none      VOID     40 41 STEVEDORE
     * method    BYTES    40 41 STEVEDORE.free_space
     * method    BOOL     40 41 STEVEDORE.happy
     * method    BYTES    40 41 STEVEDORE.used_space
     * none      VOID     40 41 STRINGS
     * method    STRING   40 41 STRINGS.lower
     * method    STRING   40 41 STRINGS.upper
     */

Unlike VMOD functions or object methods, native type methods are never
invoked as a standalone statement:

    strings.upper();

They are only evaluated atop an expression:

    (string expression).upper();

So any VMOD named after a type, like vmod_blob, should not conflict with
native type methods in the symbol table. Unless a symbol already exists
in the MAIN namespace, like reserved keywords acl and backend.