Streamline live_*_holding

Streamline live_*_holding

(live_string_holding, live_cons_holding, live_symbol_holding)
(live_float_p, live_vector_holding):
Assert that m->type is correct, instead of testing this at
runtime.  All callers changed.
(live_large_vector_holding, live_small_vector_holding):
Now two functions instead of the old live_vector_holding.
All callers changed.
(live_large_vector_p, live_small_vector_p):
Now two functions instead of the old live_vector_p.
All callers changed.
(mark_maybe_object): Ignore Lisp_Type_Unused0 quickly too,
since that cannot possibly be an object.
(CHECK_LIVE, CHECK_ALLOCATED_AND_LIVE):
New arg MEM_TYPE.  All callers changed.
(CHECK_ALLOCATED_AND_LIVE_SYMBOL): Simplify by combining
GC_CHECK_MARKED_OBJECTS code.