PERF: join on unordered CategoricalIndex

[lukemanley]

• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/v2.2.0.rst file if fixing a bug or adding a new feature.

existing test: test_join_with_categorical_index

import pandas as pd
import numpy as np

categories = [f"cat_{i:03}" for i in range(1000)]

idx1 = pd.CategoricalIndex(np.repeat(categories, 1000), categories=categories)
idx2 = pd.CategoricalIndex(categories[100:200], categories=reversed(categories))

df1 = pd.DataFrame({"val1": 1}, index=idx1)
df2 = pd.DataFrame({"val2": 2}, index=idx2)

%timeit df1.join(df2)

# 129 ms ± 7.93 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)   -> main
# 28.4 ms ± 1.18 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)  -> PR

[mroeschke]

Nit: Is this still relevant?

[lukemanley]

nope, forgot to remove that. Its now removed. thanks

[mroeschke]

Thanks @lukemanley