TST: [ArrowStringArray] more parameterised testing - part 1
aim to reduce diff to address https://github.com/pandas-dev/pandas/pull/39908#discussion_r585573328, but good to do as follow-up to #35259 anyway.

This also includes a change to inference, which could be broken off if not wanted as part of a TST PR.

more tests to change once fixture in play and also some parameterisation to add for the str accessor testing (which could be a precursor with xfails for ArrowStringArray or combined with PR that adds the accessor.. will open a draft shortly for discussion)