PERF: IntervalIndex.isin
```
In [1]: import pandas as pd

In [2]: ii = pd.IntervalIndex.from_breaks(range(100000))

In [3]: values = ii[:100]

In [4]: from pandas.core.algorithms import isin

In [5]: %timeit isin(ii, values)
91.3 ms ± 5.24 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)  # <-- master
3.84 ms ± 57.6 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)  # <-- PR
```
ok this is fine. can you add a whatsnew note. ping on green. ping