rename {lex_pt->lex_points, pad_lex_pts_with_zeros->pad_lex_tuples_with_zeros,...

rename {lex_pt->lex_points, pad_lex_pts_with_zeros->pad_lex_tuples_with_zeros, _pad_lex_pt_with_zeros->_pad_lex_tuple_with_zeros, next_insn_lex_pt->next_insn_lex_tuple}; lex_pt actually describes multiple points, not a single point