Resolves #5076 by statically asserting the mandates for the sequence containers deque, forward_list, list, and vector.

basic_string also defines a function assign_range(), but I did not add a static assert to it: basic_string includes its own specification of assign_range() which does not provide for any Mandates ([string.assign]/16). Besides, the standard doesn't list basic_string among the sequence containers in [sequence.reqmts]/1, so it appears to me that [sequence.reqmts]/60 doesn't apply directly to basic_string.