Make the acceptable compression overhead used by MultiOrdinals configurable and default to PackedInts.FASTEST (causing it to byte align).

Closes #3623

Before this commit , this was the output of TermsFacetSearchBenchmark, on my MacBookAir:

```
------------------ SUMMARY -------------------------------
                     name      took    millis
                  terms_s      7.3s        36
              terms_map_s     28.8s       144
                  terms_l     15.9s        79
              terms_map_l     15.5s        77
                 terms_sm        1m       319
             terms_map_sm      4.9m      1491
                 terms_lm      2.7m       825
             terms_map_lm      2.7m       829
          terms_stats_s_l     37.6s       188
         terms_stats_s_lm      2.4m       722
         terms_stats_sm_l      6.5m      1958
------------------ SUMMARY -------------------------------
```

After the change to FASTEST, we have:

```
------------------ SUMMARY -------------------------------
                     name      took    millis
                  terms_s      6.9s        34
              terms_map_s     28.8s       144
                  terms_l     17.4s        87
              terms_map_l     17.6s        88
                 terms_sm       42s       210
             terms_map_sm      4.2m      1287
                 terms_lm      2.3m       714
             terms_map_lm      2.3m       716
          terms_stats_s_l     37.5s       187
         terms_stats_s_lm      1.6m       482
         terms_stats_sm_l      6.1m      1852
------------------ SUMMARY -------------------------------
```