PERF: RangeIndex.value_counts/searchsorted/to_numpy
```python
In [1]: import pandas as pd

In [2]: ri = pd.RangeIndex(100_000)

In [3]: %timeit ri.to_numpy(na_value=1)
1.29 µs ± 12.3 ns per loop (mean ± std. dev. of 7 runs, 1,000,000 loops each)  # pr
21.2 µs ± 218 ns per loop (mean ± std. dev. of 7 runs, 10,000 loops each)  # main

In [4]: %timeit ri.value_counts()
47.4 µs ± 4.41 µs per loop (mean ± std. dev. of 7 runs, 10,000 loops each)  # pr
2.75 ms ± 20.7 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)  # main

In [5]: %timeit ri.searchsorted(2500)
4.14 µs ± 22.4 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)  # pr
5.03 µs ± 18 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)  # main
```
Going to merge, but happy to follow up if needed