ENH: support addition with pyarrow string dtypes

[jbrockmendel]

@mroeschke it wouldn't surprise me if you say you prefer to explicitly not support addition this way, but this seems like a pretty big use case, and the _libs.ops functions are a pretty great fit.

[mroeschke]

Just a merge conflict, otherwise LGTM

[mroeschke]

=================================== FAILURES ===================================
________________________________ test_str_join _________________________________
[gw1] linux -- Python 3.8.16 /home/runner/micromamba/envs/test/bin/python3.8

    @pytest.mark.xfail(
        reason="TODO: StringMethods._validate should support Arrow list types",
        raises=AttributeError,
    )
    def test_str_join():
        ser = pd.Series(ArrowExtensionArray(pa.array([list("abc"), list("123"), None])))
>       result = ser.str.join("=")

raises should change to a NotImplementedError it appears (which is better IMO)

[mroeschke]

Nevermind it looks like this was fixed in #51441

[mroeschke]

pandas/core/arrays/arrow/array.py:472: error: List item 0 has incompatible type "bytes"; expected "str"  [list-item]

[jbrockmendel]

greenish

[mroeschke]

Thanks @jbrockmendel