PERF: Series.str.get_dummies for "string[pyarrow]" and "string[pyarrow_numpy]" dtypes

[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.

from asv_bench.benchmarks.strings import Dummies

dtype = "string[pyarrow]"
b = Dummies()
b.setup(dtype)

%timeit b.time_get_dummies(dtype)

# 845 ms ± 51.3 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)     -> main
# 85.5 ms ± 4.44 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)  -> PR

[mroeschke]

Thanks @lukemanley