add access benchmark for columnar

[PSeitz]

multi sparse 1/13
access_values_for_doc        Avg: 12.6985ms (+0.74%)    Median: 12.5761ms (+1.02%)    [12.5325ms .. 15.6811ms]    
access_first_vals            Avg: 8.0852ms (-0.12%)     Median: 8.0347ms (+0.34%)     [7.9755ms .. 9.5182ms]      
multi 2x
access_values_for_doc        Avg: 25.1906ms (+0.89%)    Median: 25.1214ms (+0.75%)    [25.0799ms .. 26.6412ms]    
access_first_vals            Avg: 14.2296ms (-0.44%)    Median: 14.2211ms (+0.20%)    [14.1773ms .. 14.4981ms]    
sparse 1/13
access_values_for_doc        Avg: 40.5447ms (-0.15%)    Median: 40.6281ms (-0.07%)    [40.2593ms .. 40.7071ms]    
access_first_vals            Avg: 43.3743ms (+0.17%)    Median: 43.3775ms (+0.19%)    [43.2441ms .. 43.5812ms]    
dense 1/12
access_values_for_doc        Avg: 7.1800ms (+3.42%)    Median: 7.1789ms (+3.44%)    [7.1678ms .. 7.2023ms]    
access_first_vals            Avg: 6.6070ms (+1.22%)    Median: 6.6100ms (+1.29%)    [6.5745ms .. 6.6463ms]    
full
access_values_for_doc        Avg: 9.5824ms (-27.24%)    Median: 9.5755ms (-27.22%)    [9.4312ms .. 9.6552ms]    
access_first_vals            Avg: 4.4663ms (-0.03%)     Median: 4.4626ms (-0.06%)     [4.4481ms .. 4.5440ms]    

merge_multi_and_multi          Avg: 4.0975ms (+3.37%)    Median: 4.0034ms (+1.12%)    [3.9157ms .. 4.8621ms]     
merge_dense_and_dense          Avg: 0.6811ms (-0.94%)    Median: 0.6706ms (-1.97%)    [0.6584ms .. 0.9537ms]     
merge_sparse_and_sparse        Avg: 0.5703ms (-2.69%)    Median: 0.5667ms (-2.62%)    [0.5568ms .. 0.6408ms]     
merge_sparse_and_dense         Avg: 0.6318ms (+1.09%)    Median: 0.6134ms (-1.95%)    [0.6039ms .. 0.8290ms]     
merge_multi_and_dense          Avg: 5.5281ms (+2.09%)    Median: 5.4526ms (+0.82%)    [5.3714ms .. 6.3027ms]     
merge_multi_and_sparse         Avg: 8.0196ms (+2.09%)    Median: 7.8989ms (+0.85%)    [7.8592ms .. 10.2500ms]