Add gbenchmark for strings contains_re/count_re functions

[davidwendt]

Reference #5698
This creates a gbenchmark for the cudf::strings::contains_re and cudf::strings::count_re. The device logic is mostly the same for cudf::strings::contains_re and cudf::strings::matches_re so matches_re will be covered as well.

Also included here is a small change to the regex code where it fast-forwards the current character position iterator in certain cases. Using a increment approach vs recreating the iterator at the new position improved performance by ~20% for strings that contain non-ASCII UTF-8 characters.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (branch-0.19@a08ec0e). Click here to learn what that means.
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[kkraus14]

CMake lgtm

[davidwendt]

@gpucibot merge